Method for installing a self-floating deck structure onto a buoyant substructure

ABSTRACT

This invention provides a method for installing a self-floating deck structure with at least one recessed cavity on the bottom of the self-floating deck structure onto a buoyant substructure. The self-floating deck structure is aligned over a submerged buoyant substructure and the top of the buoyant substructure is inserted into a recessed cavity in the self-floating deck structure until the buoyant substructure mates with the self-floating deck structure at a point above the water surface. The self-floating deck and the buoyant substructure are connected by welding or one or more mechanical device.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent application is a continuation-in-part patent application of pending non-provisional patent application U.S. Serial No. 10/368,629 filed on Feb. 20, 2003 from prior provisional patent application U.S. Serial No. 60/410,310 filed on Sep. 13, 2002 both of which are incorporated by reference in their entireties herein. This application also incorporates by reference Disclosure Document No. 534764 filed on Jul. 15, 2003.

[0002] This application claims priority from both of the aforementioned patent applications.

BACKGROUND OF THE INVENTION

[0003] I. Field of the Invention

[0004] The present invention is related to a method for installing a self-floating deck structure onto a buoyant substructure of an offshore platform, such as is used in the exploitation of petroleum reserves.

[0005] In the past, installation of offshore deck structures generally required the use of a floating barge or vessel with a large crane to lift the deck structure and place it on the substructure. This method has numerous shortcomings, including the high cost of the barge or vessel mounted cranes and scheduling the availability of such barges or vessels. In some cases, the deck structure is so heavy that the structures cannot be lifted in one piece and have to be installed in multiple lifts. A deck structure installed by barge or vessel mounted cranes often require additional structural reinforcement to withstand the forces attributable to the lifting of the deck structures. These factors increase the overall cost of the project by increasing material and construction costs, and hookup and commissioning work offshore, which significantly increases the expense of the project.

[0006] Recently integrated float over decks have been installed in various locations. These installations have typically utilized a deck mounted on a barge or barges to transport the deck structure to the installation location. Once at the installation site in the case where a single barge is utilized, the barge is typically positioned between the legs of the supporting structure. The deck structure is then lowered onto the legs of the support structure, typically either by ballasting the barge or by lowering jacks that support the deck structure on the barge.

[0007] In some instances a specifically designed barge can be utilized which can be positioned around or outside of the legs of the support structure. However, it increases the installation cost of the project to build a new barge or to modify an existing barge for such a purpose.

[0008] In other instances multiple barges can be utilized to transport and install the deck structure. When multiple barges are utilized they usually are positioned outside of the legs of the support structure that is fixed to the seabed. The barges are then ballasted to lower the deck onto the legs of the support structure. Alternatively, the deck structure can be mounted on jacks that are installed on the barges and the jacks can lower the deck structure onto the support structure.

[0009] The use of multiple barges can also be utilized to install a deck over a buoyant substructure. The deck structure mounted on multiple barges can then be positioned over a buoyant substructure that has been sufficiently ballasted to create clearance between the top of the buoyant substructure and the bottom of the deck structure. Once the deck is correctly aligned over the buoyant substructure, the substructure can be deballasted until the top of the substructure mates with the deck structure. The deballasting can continue until the deck structure is installed at the correct elevation above the water surface. The disadvantage of this method is the decrease in stability due to the use of multiple barges. The method is also susceptible to delays and potential damage to the deck structure and buoyant substructure due to wave action or swells.

SUMMARY OF THE INVENTION

[0010] The present invention provides a method to install a self-floating deck structure onto a buoyant substructure. A line connected to a lifting device located on the self-floating deck structure is lowered from the self-floating deck structure through a recessed cavity in the bottom of the deck structure and connected to the top surface of the buoyant substructure. The buoyant substructure is then sufficiently submerged below the water surface by ballasting until the top surface of the buoyant substructure is below the bottom surface of the self-floating deck structure to allow the self-floating deck structure to be positioned over the submerged buoyant substructure. The line connected to the lifting device supports the submerged buoyant substructure to prevent it from sinking deeper than is required for installing the self-floating deck structure onto the buoyant substructure. The recessed cavity of the self-floating deck structure is positioned and aligned over the submerged buoyant substructure and the lifting device retracts the line to lift the buoyant substructure until the top surface of the buoyant substructure is inserted within the recessed cavity of the self-floating deck structure and mates with the ceiling surface of the recessed cavity of the self-floating deck structure above the water surface. The buoyant substructure is then deballasted to raise the self-floating deck structure to a predetermined elevation above the water surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a further understanding of the nature of the present invention reference should be made to the following detailed description, taken in conjunction with the accompanying drawings in which like parts are given like reference numerals, and wherein:

[0012]FIG. 1a is a side view of a self-floating deck structure.

[0013]FIG. 1b is a plan view of a self-floating deck structure.

[0014]FIG. 2 is a side view of a buoyant substructure after it has been installed by mooring it to the seabed.

[0015]FIG. 3 is a side view of a self-floating deck structure connected by a lifting line present on a lifting device to an adjacent buoyant substructure.

[0016]FIG. 4 illustrates a buoyant substructure submerged below the water surface while adjacent to a self-floating deck structure.

[0017]FIG. 5 illustrates a self-floating deck structure positioned over a submerged buoyant substructure with the submerged buoyant substructure suspended below the self-floating deck structure by the lifting device.

[0018]FIG. 6 illustrates a buoyant substructure after it has been raised by a lifting device to contact the mating surface of a self-floating deck structure.

[0019]FIG. 7 illustrates a buoyant substructure connected to a self-floating deck structure at the correct installed elevation.

[0020]FIG. 8 illustrates an alternative embodiment of the inventive method where the water has been displaced from the recessed cavity of the self-floating deck structure by pumping compressed air (or other gas) into the recessed cavity.

[0021]FIG. 9 illustrates an alternative embodiment of the inventive method showing a self-floating deck structure in which the sides of the recessed cavity of the self-floating deck structure taper inward from the bottom of the self-floating deck structure towards the top of the recessed cavity.

[0022]FIG. 10 illustrates an alternative embodiment of the inventive method showing the buoyant substructure where the sides of the buoyant substructure taper inward from the outer surface of the substructure.

[0023]FIG. 11a illustrates a plan view of an alternative embodiment of the inventive method showing a self-floating deck structure that is supported by four deck support legs.

[0024]FIG. 11b illustrates a side view of an alternative embodiment of the inventive method showing a buoyant substructure with four deck support legs.

[0025]FIG. 11c illustrates a plan view of an alternative embodiment of the inventive method showing a buoyant substructure with four deck support legs.

[0026]FIG. 12a illustrates an alternative embodiment of the inventive method showing a self-floating deck structure adjacent to a buoyant substructure having multiple deck support legs.

[0027]FIG. 12b illustrates an alternative embodiment of the inventive method showing a buoyant substructure with multiple deck support legs suspended below the self-floating deck structure from the lifting device.

[0028]FIG. 13 illustrates an alternative embodiment of the inventive method showing a buoyant substructure positioned on the seabed.

[0029]FIG. 14 illustrates an alternative embodiment of the inventive method showing the buoyant substructure sidewall mated with the recessed cavity sidewall.

[0030]FIG. 15a illustrates the submerged buoyant substructure being supported by a plurality of floating vessels having lines connected to the buoyant substructure. FIG. 15b illustrates a plurality of buoyancy tanks to support the buoyant substructure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0031] In a first aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure said method comprising the steps of:

[0032] (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity;

[0033] (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0034] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0035] (d) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each line to the buoyant substructure;

[0036] (e) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from the self-floating deck structure by at least one lifting line connected to at least one lifting device;

[0037] (f) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0038] (g) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0039] (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0040] (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0041] In a second aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure said method comprising the steps of:

[0042] (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity;

[0043] (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming a circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity present in the self-floating deck structure;

[0044] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0045] (d) connecting at least one lifting line connected to at least one lifting device located on the-self-floating deck structure to the buoyant substructure;

[0046] (e) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from the self-floating deck structure by at least one lifting line connected to at least one lifting device;

[0047] (f) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface present on the buoyant substructure;

[0048] (g) activating each lifting device to retract each connected lifting line and lift the buoyant substructure up until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface;

[0049] (h) connecting the self-floating deck structure to the buoyant substructure by welding or by a plurality of mechanical devices; and

[0050] (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0051] In a third aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure said method comprising the steps of:

[0052] (a) providing a self-floating deck structure, said self-floating deck structure having a bottom surface and a recessed cavity extending upward from the bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming an upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity;

[0053] (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0054] (c) positioning the self-floating deck structure adjacent to said buoyant substructure and connecting at least one lifting line connected to at least one lifting device located on the self-floating deck structure to the buoyant substructure;

[0055] (d) ballasting the buoyant substructure below the water surface until the buoyant substructure bottom surface rests upon a seabed present in the water deep enough so that the buoyant substructure top surface is below the bottom surface of the self-floating deck structure;

[0056] (e) positioning the self-floating deck structure over the submerged buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0057] (f) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity of the self-floating deck structure until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0058] (g) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0059] (h) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface suitable for towing the connected self-floating deck structure and buoyant substructure to a final installation location.

[0060] In a fourth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure said method comprising the steps of:

[0061] (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming an upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity;

[0062] (b) providing a buoyant substructure that has a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming at least one circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity of the self-floating deck structure;

[0063] (c) positioning the self-floating deck structure adjacent to said buoyant substructure and connecting at least one lifting line connected to at least one lifting device present on the self-floating deck structure to the buoyant substructure;

[0064] (d) ballasting the buoyant substructure below the water surface until the buoyant substructure bottom surface rests upon a seabed present in the water deep enough so that each deck support leg top surface is positioned below the bottom surface of the self-floating deck structure;

[0065] (e) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure is aligned over a deck support leg top surface of the buoyant substructure;

[0066] (f) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure up until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with the recessed cavity ceiling-surface at a point above the water surface;

[0067] (g) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0068] (h) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0069] In a fifth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure said method comprising the steps of:

[0070] (a) providing a self-floating deck structure with a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an opened end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity;

[0071] (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and said buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming at least one upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0072] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0073] (d) providing at least one line that is connected to the self-floating deck structure;

[0074] (e) connecting each line to the buoyant substructure;

[0075] (f) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from the self-floating deck structure by at least one line;

[0076] (g) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0077] (h) raising the buoyant substructure top surface up into the recessed cavity by adjusting the buoyancy of the buoyant substructure until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0078] (i) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical device; and

[0079] (j) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0080] In a sixth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure said method comprising the steps of:

[0081] (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above the water surface, the intersection of the recessed cavity sidewalls and the recessed cavity ceiling surfaces forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewalls and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity;

[0082] (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure bottom surface, each deck support leg having a deck support leg top surface and a deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming at least one circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity of the self-floating deck structure;

[0083] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0084] (d) providing at least one line that is connected to said self-floating deck structure;

[0085] (e) connecting each line to the buoyant substructure;

[0086] (f) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg of the buoyant substructure is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from at least one line connected to the self-floating deck structure;

[0087] (g) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface of the buoyant substructure;

[0088] (h) raising the buoyant substructure up by adjusting the buoyancy of the buoyant substructure until each of deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface;

[0089] (i) connecting the self-floating deck structure to the buoyant substructure of the self-floating deck structure by welding or by one or more mechanical devices; and

[0090] (j) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0091] In a seventh aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure said method comprising the steps of:

[0092] (a) providing a self-floating deck structure, said self-floating deck structure having a bottom surface and a recessed cavity extending upward from the bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above the water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity;

[0093] (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming at least one upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0094] (c) positioning the self-floating deck structure adjacent to said buoyant substructure that has been ballasted below the water surface so that the buoyant substructure bottom surface rests on a seabed present in the water deep enough such that the buoyant substructure top surface is below the bottom surface of the self-floating deck structure;

[0095] (d) positioning the self-floating deck structure over the submerged buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0096] (e) raising the buoyant substructure top surface up into the recessed cavity of the self-floating deck structure by adjusting the buoyancy of the buoyant substructure until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0097] (f) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0098] (g) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface suitable for towing the connected self-floating deck structure and buoyant substructure to a final installation location.

[0099] In an eighth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure said method comprising the steps of:

[0100] (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above the water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity;

[0101] (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming at least one circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity of the self-floating deck structure;

[0102] (c) ballasting the buoyant substructure below the water surface until the buoyant substructure bottom surface rests on a seabed present in the water deep enough so that each deck support leg top surface is below the bottom surface of the self-floating deck structure;

[0103] (d) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface of the buoyant substructure;

[0104] (e) raising the buoyant substructure up by adjusting the buoyancy of the buoyant substructure until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface;

[0105] (f) connecting the self-floating deck structure to the buoyant substructure of the self-floating deck structure by welding or by one or more mechanical devices; and

[0106] (g) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0107] In a ninth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure said method comprising the steps of:

[0108] (a) providing a self-floating deck structure with a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, a recessed cavity ceiling surface at least one recessed cavity sidewall, said recessed cavity ceiling surface being positioned above the water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity, the dimension of the upper circumferential edge of the recessed cavity being smaller than the dimension of the lower circumferential edge of the recessed cavity causing the recessed cavity sidewall to taper inward as it progresses from said lower circumferential edge of the recessed cavity towards said upper circumferential edge of the recessed cavity;

[0109] (b) providing a buoyant substructure that is capable of being fully submerged below a water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming at least one upper circumferential edge of the buoyant substructure, the circumferential dimension of the buoyant substructure top surface being larger than the circumferential dimension of the recessed cavity ceiling surface but smaller than the circumferential dimension of the lower circumferential edge of the recessed cavity, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted to fit within the recessed cavity of the self-floating deck structure, and being sized so that the buoyant substructure sidewall mates snugly with the recessed cavity sidewall when the buoyant substructure top surface is inserted in the recessed cavity;

[0110] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0111] (d) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each line to the buoyant substructure;

[0112] (e) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from the self-floating deck structure by at least one lifting line connected to at least one lifting device;

[0113] (f) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0114] (g) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity using at least one lifting device until the buoyant substructure sidewall mates with the recessed cavity sidewall;

[0115] (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0116] (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0117] In a tenth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure said method comprising the steps of:

[0118] (a) providing a self-floating deck structure with a bottom surface and at least one recessed cavity extending upward from said bottom surface of the self-floating deck structure, each recessed cavity comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each recessed cavity ceiling surface being positioned above the water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity;

[0119] (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming at least one circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity of the self-floating deck structure;

[0120] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0121] (d) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each line to the buoyant substructure;

[0122] (e) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from the self-floating deck structure by at least one lifting line connected to at least one lifting device;

[0123] (f) positioning the self-floating deck structure over the buoyant substructure so that at least one recessed cavity of the self-floating deck structure is aligned over a plurality of deck support leg top surfaces of the buoyant substructure;

[0124] (g) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure up until a plurality of deck support leg top surfaces are inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface;

[0125] (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0126] (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0127] In an eleventh aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0128] (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity;

[0129] (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0130] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0131] (d) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure;

[0132] (e) providing at least one buoyancy tank, each buoyancy tank having at least one line having one end connected to said buoyancy tank and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface;

[0133] (f) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from at least one buoyancy tank by at least one line connected to at least one buoyancy tank;

[0134] (g) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0135] (h) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity using at least one lifting device until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0136] (i) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0137] (j) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0138] In a twelfth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0139] (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity;

[0140] (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0141] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0142] (d) providing at least one buoyancy tank, each buoyancy tank having at least one line having one end connected to said buoyancy tank and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface;

[0143] (e) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from at least one buoyancy tank by at least one line connected to at least one buoyancy tank;

[0144] (f) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0145] (g) raising the buoyant substructure top surface up into the recessed cavity by adjusting the buoyancy of the buoyant substructure until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0146] (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0147] (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0148] In a thirteenth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0149] (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity;

[0150] (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0151] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0152] (d) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure;

[0153] (e) providing at least one floating vessel, each floating vessel having at least one line having one end connected to said floating vessel and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface;

[0154] (f) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from at least one floating vessel by at least one line connected to at least one floating vessel;

[0155] (g) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0156] (h) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity using at least one lifting device until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0157] (i) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0158] (j) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0159] In a fourteenth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0160] (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity;

[0161] (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0162] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0163] (d) providing at least one floating vessel, each floating vessel having at least one line having one end connected to said floating vessel and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface;

[0164] (e) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from at least one floating vessel by at least one line connected to at least one floating vessel;

[0165] (f) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0166] (g) raising the buoyant substructure top surface up into the recessed cavity by adjusting the buoyancy of the buoyant substructure until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0167] (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0168] (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0169] In a fifteenth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0170] (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity;

[0171] (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0172] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0173] (d) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure;

[0174] (e) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0175] (f) lowering lifting means from one or more lifting devices positioned on said self-floating deck structure and connecting said lifting means to said buoyant substructure;

[0176] (g) activating the lifting device to retract the lifting means and lift the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0177] (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0178] (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0179] In a sixteenth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0180] (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity;

[0181] (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming a circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity present in the self-floating deck structure;

[0182] (c) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0183] (d) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg is below the bottom surface of the self-floating deck structure;

[0184] (e) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface present on the buoyant substructure;

[0185] (f) lowering lifting means from one or more lifting device positioned on said self-floating deck structure and connecting said lifting means to said buoyant substructure;

[0186] (g) activating the lifting device to retract the lifting means and lift the buoyant substructure up until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface;

[0187] (h) connecting the self-floating deck structure to the buoyant substructure by welding or by a plurality of mechanical devices; and

[0188] (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0189] In a seventeenth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0190] (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity;

[0191] (b) providing a buoyant frame that is capable of being fully submerged below the water surface, said buoyant frame having a buoyant frame top surface and a buoyant frame bottom surface, said buoyant frame further having an opening extending through said buoyant frame from said buoyant frame top surface to said buoyant frame bottom surface, said opening being sized and shaped to allow a buoyant substructure to be positioned within said opening;

[0192] (c) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface, said buoyant substructure further having a buoyant substructure base member that has perimetric dimensions greater than the perimetric dimensions of the opening in the buoyant frame, said buoyant substructure base member having a top face, said buoyant substructure having at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0193] (d) positioning said buoyant substructure within said opening in said buoyant frame;

[0194] (e) connecting said buoyant frame to a seabed by mooring means;

[0195] (f) submerging said buoyant frame below the water surface at a predetermined design depth;

[0196] (g) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0197] (h) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure;

[0198] (i) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure;

[0199] (j) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0200] (k) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0201] (l) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0202] (m) deballasting the buoyant substructure until the top face of the buoyant substructure base member mates with the buoyant frame bottom surface;

[0203] (n) connecting said buoyant frame to said buoyant substructure by welding or by one or more mechanical device;

[0204] (o) raising the self-floating deck structure to a predetermined elevation above the water surface by adjusting said mooring means or deballasting said buoyant substructure or said buoyant frame.

[0205] In a eighteenth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0206] (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity;

[0207] (b) providing a buoyant frame that is capable of being fully submerged below the water surface, said buoyant frame having a buoyant frame top surface and a buoyant frame bottom surface, said buoyant frame further having an opening extending through said buoyant frame from said buoyant frame top surface to said buoyant frame bottom surface, said opening being sized and shaped to allow a buoyant substructure to be positioned within said opening;

[0208] (c) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface, said buoyant substructure further having a buoyant substructure base member that has perimetric dimensions greater than the perimetric dimensions of the opening in the buoyant frame, said buoyant substructure base member having a top face, said buoyant substructure at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0209] (d) positioning said buoyant substructure within said opening in said buoyant frame;

[0210] (e) connecting said buoyant frame to a seabed by mooring means;

[0211] (f) submerging said buoyant frame below the water surface to a predetermined design depth;

[0212] (g) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure;

[0213] (h) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0214] (i) lowering drill pipe from a drilling rig located on the self-floating deck structure and connecting the drill pipe to the buoyant substructure;

[0215] (j) activating the drilling rig to retract the drill pipe and lift the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0216] (k) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0217] (l) deballasting the buoyant substructure until the top face of the buoyant substructure base member mates with the buoyant frame bottom surface;

[0218] (m) connecting said buoyant frame to said buoyant substructure by welding or by one or more mechanical device;

[0219] (n) raising the self-floating deck to a predetermined elevation above the water surface by adjusting said mooring means or by deballasting said buoyant substructure or said buoyant frame.

[0220] In a nineteenth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0221] (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity;

[0222] (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming a circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity present in the self-floating deck structure;

[0223] (c) providing a buoyant frame that is capable of being fully submerged below the water surface, said buoyant frame having a buoyant frame top surface and a buoyant frame bottom surface, said buoyant frame further having a plurality of openings extending through said buoyant frame from said buoyant frame top surface to said buoyant frame bottom surface, said openings being sized and shaped to allow a deck support leg to be positioned within said opening;

[0224] (d) positioning each deck support leg within an opening in said buoyant frame;

[0225] (e) connecting said buoyant frame to a seabed by mooring means;

[0226] (f) submerging said buoyant frame below the water surface at a predetermined design depth;

[0227] (g) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0228] (h) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure;

[0229] (i) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg is below the bottom surface of the self-floating deck structure;

[0230] (j) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface present on the buoyant substructure;

[0231] (k) activating each lifting device to retract the connected lifting line and lift the buoyant substructure up until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface;

[0232] (l) connecting the self-floating deck structure to the buoyant substructure by welding or by a plurality of mechanical devices;

[0233] (m) deballasting the buoyant substructure until the top face of the buoyant substructure base member mates with the buoyant frame bottom surface;

[0234] (n) connecting said buoyant frame to said buoyant substructure by welding one or more mechanical device; and

[0235] (o) raising the self-floating deck structure to a predetermined elevation above the water surface by adjusting said mooring means or deballasting said buoyant substructure or said buoyant frame.

[0236] In a twentieth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0237] (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity;

[0238] (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming a circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity present in the self-floating deck structure;

[0239] (c) providing a buoyant frame that is capable of being fully submerged below the water surface, said buoyant frame having a buoyant frame top surface and a buoyant frame bottom surface, said buoyant frame further having a plurality of openings extending through said buoyant frame from said buoyant frame top surface to said buoyant frame bottom surface, said openings being sized and shaped to allow a deck support leg through said opening;

[0240] (d) positioning each deck support leg within an opening in said buoyant frame;

[0241] (e) connecting said buoyant frame to a seabed by mooring means;

[0242] (f) submerging said buoyant frame below the water surface to a predetermined design depth;

[0243] (g) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg is below the bottom surface of the self-floating deck structure;

[0244] (h) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface present on the buoyant substructure;

[0245] (i) lowering lifting means from at least one lifting device located on the self-floating deck structure and connecting the lifting means to the buoyant substructure;

[0246] (j) activating at least one lifting device to retract the lifting means and lift the buoyant substructure up until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface;

[0247] (k) connecting the self-floating deck structure to the buoyant substructure by welding or by a plurality of mechanical devices;

[0248] (l) deballasting the buoyant substructure until the top face of the buoyant substructure base member mates with the buoyant frame bottom surface;

[0249] (m) connecting said buoyant frame to said buoyant substructure by welding or one or more mechanical device; and

[0250] (n) raising the self-floating deck to a predetermined elevation above the water surface by adjusting said mooring means or deballasting said buoyant substructure or said buoyant frame.

[0251] In a twenty-first aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0252] (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity;

[0253] (b) providing a base structure that is capable of being fully submerged below the water surface, said base structure having a base structure top surface and a base structure bottom surface, said base structure further having a base structure opening extending through said base structure from said base structure top surface to said base structure bottom surface, said base structure opening being sized and shaped to allow a buoyant substructure to be positioned within said base structure opening, said base structure further comprising a hollow tube extending upward from said base structure top surface in vertical alignment with said base structure opening;

[0254] (c) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface, said buoyant substructure further having a buoyant substructure base member that has perimetric dimensions greater than the perimetric dimensions of the opening in the buoyant frame, said buoyant substructure base member having a top face, said buoyant substructure having at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0255] (d) positioning said buoyant substructure within said hollow tube and connecting said buoyant substructure to said base structure with connecting means;

[0256] (e) positioning said base structure on the seabed at an installation site;

[0257] (f) securing said base structure to said seabed;

[0258] (g) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0259] (h) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure;

[0260] (i) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure;

[0261] (j) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0262] (k) activating at least one lifting device to retract the connected lifting line and lifting the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0263] (l) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices;

[0264] (m) raising the self-floating deck structure to a predetermined elevation above the water surface by deballasting said buoyant substructure; and

[0265] (n) connecting said buoyant substructure to said hollow tube by grouting, welding or by one or mechanical connector.

[0266] In a twenty-second aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0267] (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity;

[0268] (b) providing a buoyant frame that is capable of being fully submerged below the water surface, said buoyant frame having a buoyant frame top surface and a buoyant frame bottom surface, said buoyant frame further having an opening extending through said buoyant frame top surface to said buoyant frame bottom surface, said opening being sized and shaped to allow a buoyant substructure to be positioned within said opening, said buoyant frame further having a hollow tube extending upward from said buoyant frame top surface in vertical alignment with said opening;

[0269] (c) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface, said buoyant substructure further having a buoyant substructure base member that has perimetric dimensions greater than the perimetric dimensions of the opening in the buoyant frame, said buoyant substructure base member having a top face, said buoyant substructure having at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure;

[0270] (d) positioning said buoyant substructure at least partially within said hollow tube;

[0271] (e) connecting said buoyant frame to a seabed by mooring means;

[0272] (f) submerging said buoyant frame below the water surface at a predetermined design depth;

[0273] (g) positioning said self-floating deck structure adjacent to said buoyant substructure;

[0274] (h) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure;

[0275] (i) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure;

[0276] (j) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface;

[0277] (k) activating at least one lifting device to retract the connected lifting line and lifting the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface;

[0278] (l) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices;

[0279] (m) raising the self-floating deck structure to a predetermined elevation above the water surface by adjusting said mooring means or deballasting said buoyant substructure or buoyant frame; and

[0280] (n) connecting said buoyant substructure to said hollow tube by grouting, welding or by one or mechanical connector.

[0281] In a twenty-third aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0282] (o) providing a self-floating deck structure having a bottom surface, said self-floating deck structure having at least two hulls extending from the bottom surface, said hulls being sized and shaped to provide buoyancy for the self-floating deck such that the bottom surface is positioned above the water surface, said hulls further being sized and shaped such that the self-floating deck structure can be positioned over a buoyant substructure such that the bottom surface of the self-floating deck structure does not collide with the buoyant substructure top surface;

[0283] (p) providing a buoyant substructure, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall;

[0284] (q) positioning said self-floating deck structure over said buoyant substructure;

[0285] (r) lowering at least one lifting means connected to at least one lifting device located on the self-floating deck structure and connecting each lifting means to the buoyant substructure;

[0286] (s) activating at least one lifting device to retract the connected lifting means and lift the buoyant substructure top surface up until the buoyant substructure top surface mates with the bottom surface;

[0287] (t) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and

[0288] (u) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0289] In a twenty-fourth aspect the present invention provides for a method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of:

[0290] (a) providing a self-floating deck structure having a bottom surface, said self-floating deck structure having at least two hulls extending from the bottom surface, said hulls being sized and shaped to provide buoyancy for the self-floating deck such that the bottom surface is positioned above the water surface, said hulls further being sized and shaped such that the self-floating deck structure can be positioned over a buoyant substructure such that the bottom surface of the self-floating deck structure does not collide with a buoyant substructure top surface;

[0291] (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, each deck support leg having a deck support leg top surface;

[0292] (c) positioning said self-floating deck structure over said deck support legs of said buoyant substructure;

[0293] (d) connecting at least one lifting means connected to at least one lifting device located on the self-floating deck structure to the buoyant substructure;

[0294] (e) activating at least one lifting device to retract the lifting means and lift the buoyant substructure up until each deck support leg top surface mates with the bottom surface of the self-floating deck structure;

[0295] (f) connecting the self-floating deck structure to the buoyant substructure by welding or by a plurality of mechanical devices; and

[0296] (g) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.

[0297] Specific methods within the scope of the present invention include, but are not limited to, the methods discussed in detail herein and/or illustrated in the drawings that are present herein.

[0298] Contemplated equivalents of the methods described and illustrated herein and/or illustrated in the drawings contained herein include methods which otherwise correspond thereto, and which have the same general properties and/or components thereof, wherein one or more simple or other variations of components, materials or steps are made.

[0299] All of the structures and components used to carry out the methods of the present invention, such as self-floating deck structures, buoyant substructures, lifting devices and lines, are commercially available from sources known by those of ordinary skill in the art.

[0300] For the purpose of illustrating structures that may be employed in the methods of the present invention, there are shown in the drawings, which form a material part of this disclosure, different views of various self-floating deck structures and buoyant substructures that may be employed in the methods of the present invention.

[0301] The different components of the various self-floating deck structures and buoyant substructures that may be employed in the methods of the present invention may be generally arranged in the manner shown in the drawings, or described hereinbelow. However, the present invention is not limited to methods employing self-floating deck structures and buoyant substructures having the precise arrangements, configurations, dimensions and/or instrumentalities shown in these drawings, or described hereinbelow. These arrangements, configurations, dimensions and instrumentalities may be otherwise, as circumstances require.

[0302] Different specific embodiments of self-floating deck structures and buoyant substructures that may be employed in the methods of the present invention will now be described with reference to the drawings.

[0303] As shown in FIG. 1a and FIG. 1b, the self-floating deck structure 10 has a recessed cavity 11 extending upward into the self-floating deck structure 10 from the bottom surface 12 of the self-floating deck structure 10 having circumferential dimensions that are slightly larger than the circumference of the buoyant substructure top surface 21. The recessed cavity 11 is formed by an open end 18, at least one recessed cavity sidewall 17 and a recessed cavity ceiling surface 14. The intersection of the recessed cavity sidewall 17 and the recessed cavity ceiling surface 14 forms an upper circumferential edge 19 of the recessed cavity 11. The intersection of the recessed cavity sidewall 17 and the bottom surface 12 of the self-floating deck structure 10 forms at least one lower circumferential edge 13 of the recessed cavity 11. The lower circumferential edge 13 of the recessed cavity 11 is preferably rounded to facilitate the insertion of the buoyant substructure top surface 21. into the recessed cavity 11 of the self-floating deck structure 10. The upper circumferential edge 19 of the recessed cavity 11 present in the self-floating deck structure 10 is also preferably rounded to facilitate the mating of the buoyant substructure top surface 21 to the recessed cavity 11 ceiling surface 14. Although, in a preferred embodiment of the methods of the present invention, the upper 19 and lower 13 circumferential edges of the recessed cavity 11 are rounded, the inventive method can be practiced without the upper 19 or lower 13 circumferential edges of the recessed cavity 11 being rounded. The circumferential dimensions of the upper and lower circumferential edges of the recessed cavity of the buoyant substructure can vary widely as is known by those skilled in the art.

[0304] As is shown in FIG. 2 the buoyant substructure 20 may be installed and connected to a seabed 30 located below the water surface 35 by mooring means 40 prior to the commencement of the deck installation. The mooring means 40 can include chain, cable, wire, rope, pipe or tension leg tendons. Although it is preferable to do this, it is recognized that the inventive methods can be practiced without the buoyant substructure 20 being previously installed at a permanent location. The buoyant substructure 20 has a buoyant substructure top surface 21 and a buoyant substructure bottom surface 24. The buoyant substructure top surface 21 and the buoyant substructure bottom surface 24 are connected by at least one buoyant substructure sidewall 25. The intersection of the buoyant substructure top surface 21 and the buoyant substructure sidewall 25 form an upper circumferential edge 22 of the buoyant substructure 20. The buoyant substructure top surface 21 and the buoyant substructure sidewall 25 adjacent to the buoyant substructure top surface 21 are adapted and sized to fit within the recessed cavity 11 of the self-floating deck structure 10. The upper circumferential edge 22 of the buoyant substructure top surface 21 preferably has a rounded shape to facilitate the insertion of the buoyant substructure top surface 21 into the recessed cavity 11 of the self-floating deck structure 10. Although the preferred embodiment of the methods of the present invention utilizes a rounded upper circumferential edge 22 of the buoyant substructure 20, the inventive methods can be practiced without the upper circumferential edge 22 being rounded. The circumferential dimension of the upper circumferential edge of the buoyant substructure can vary widely as known by those skilled in the art. It is recognized that the inventive methods are also suitable for installing a self-floating deck structure 10 onto a buoyant substructure 20 prior to the buoyant substructure 20 being installed at its permanent installation location. In such a circumstance, the self-floating deck structure 10 can be installed onto the buoyant substructure 20 at a location other than the installation location. The combined buoyant substructure 20 and self-floating deck structure 10 can then be towed or transported to a final location where the combined structure can be installed.

[0305] Referring to FIG. 3, the self-floating deck structure 10 is positioned adjacent to the buoyant substructure 20, which has previously been installed. A lifting line 15 connected to a lifting device 16 is lowered from the lifting device 16, which is preferably located on the top 9 of the self-floating deck structure 10, and is connected to the top surface 21 of the buoyant substructure 20. In a preferred embodiment, a single lifting line 15 is utilized. However, it is recognized that the inventive methods of this invention can be practiced using multiple lifting lines 15 and multiple lifting devices 16. The lifting line 15 connected to the lifting device 16 can be made from rope, chain, wire cable or synthetic cable, or other material that can be used with the lifting device 16. In a preferred embodiment, a winch is used as the lifting device 16, for example, to retract the lifting line 15 and lift the buoyant substructure 20. However, other suitable lifting devices 16 can be used, including a jack, a crane or drilling rig. In a preferred embodiment, the lifting device 16 is located on the top of the self-floating deck structure 10. However, it is recognized that the lifting device 16 can be placed in other locations on or within the self-floating deck structure 10. It is recognized that the inventive methods of the present invention can be practiced by utilizing a line or lines separate from that or those used to lift the buoyant substructure 20 to suspend the buoyant substructure 20 from the self-floating deck structure 10. Said lines can be chain, cable, wire or rope or other suitable material as known to those skilled in the art. It is also recognized that the inventive methods of this invention can be practiced with the lifting line 15 connected to other points on the buoyant substructure 20 other than the top surface 21.

[0306] The buoyant substructure 20 is preferably ballasted until it is completely submerged below the water surface 35, as is seen in FIG. 4. As the buoyant substructure 20 is ballasted below the water surface 35, the lifting line 15 supports the buoyant substructure 20 and preferably prevents it from sinking further than is required for the installation of the self-floating deck structure 10 onto the buoyant substructure 20.

[0307] As is shown in FIG. 5, the self-floating deck structure 10 is preferably positioned over the submerged buoyant substructure 20 until the recessed cavity 11 of the self-floating deck structure 10 is aligned over the buoyant substructure top surface 21 while the submerged buoyant substructure 20 is suspended from the self-floating deck structure 10 by the lifting line 15 connected to the lifting device 16.

[0308] As is seen in FIG. 6, the buoyant substructure top surface 21 is preferably lifted up into the recessed cavity 11 of the self-floating deck structure 10 by the lifting device 16 retracting the lifting line 15 connected thereto, lifting the buoyant substructure top surface 21 until it contacts the recessed cavity ceiling surface 14 at a point above the water surface 35. After the buoyant substructure top surface 21 has contacted the recessed cavity ceiling surface 14 the two structures can be further connected by welding or by a mechanical device or a plurality of mechanical devices.

[0309] After the buoyant substructure top surface 21 has mated with the recessed cavity ceiling surface 14 at point above the water surface 35, the buoyant substructure 20 is preferably deballasted to raise the self-floating deck structure 10 to a predetermined elevation above the water surface 35, as is illustrated in FIG. 7. The predetermined elevation is dependent upon a number of factors including but not limited to the predicted wave heights and predicted weather conditions at the installation location for the combined self-floating deck structure and buoyant substructure.

[0310] In an alternative embodiment of the methods of the present invention, as is illustrated in FIG. 8, the water in the recessed cavity 11 of the self-floating deck structure 10 can be partially or completely displaced by pumping compressed air or other gas into the recessed cavity 11. The compressed air or other gas in the recessed cavity 11 of the self-floating deck structure 10 increases the displacement of the self-floating deck structure 10 and acts as a dampener to reduce the potential for impact between the buoyant substructure top surface 21 and the recessed cavity ceiling surface 14.

[0311] In an alternative embodiment of the methods of the present invention, as is shown in FIG. 9, the circumferential dimension of the upper circumferential edge 19 of the recessed cavity 11 is preferably smaller than the circumferential dimension of the lower circumferential edge 13 of the recessed cavity 11 causing the recessed cavity sidewall 17 to taper inward from the bottom surface 12 of the self-floating deck structure 10 as it progresses towards the recessed cavity ceiling surface 14 to facilitate insertion of the buoyant substructure top surface 21 into the recessed cavity 11 of the self-floating deck structure 10.

[0312] In an alternative embodiment of the methods of the present invention, as is illustrated in FIG. 10, the circumferential dimension of the upper circumferential edge 22 of the buoyant substructure 20 is preferably smaller than the circumferential dimension of the buoyant substructure sidewall 25 adjacent to the buoyant substructure top surface 21, causing the buoyant substructure sidewall 25 adjacent to the buoyant substructure top surface 21 to taper inward as it progresses towards the buoyant substructure top surface 21.

[0313] In an alternative embodiment of the methods of the present invention, as is illustrated in FIG. 11a, the self-floating deck structure 10 has a plurality of recessed cavities 11 to accommodate the deck support leg top surface 41 of a plurality of deck support legs 43 of the buoyant substructure 20. In the embodiment shown in FIG. 11b and FIG. 11c, the buoyant substructure 20 has four deck support legs 43. It is recognized that the inventive methods are not limited to the use of four deck support legs 43, but can be practiced with some other plurality of deck support legs 43 (two, three, five, six legs, etc.).

[0314] In an alternative embodiment of the methods of the present invention, as is illustrated in FIG. 12a, a plurality of lifting lines 15 from a plurality of lifting devices 16 on the self-floating deck structure 10 are connected to the deck support leg top surfaces 41. It is understood that the methods of the present invention can be practiced such that the deck support leg top surface 41 and the deck support leg sidewall 44 adjacent to the deck support leg top surface 41 are adapted to fit within a recessed cavity 11 of the self-floating deck structure 10 and are sized so the circumferential dimension of the circumferential edge 42 of the deck support leg 43 is smaller than the circumferential dimension of the deck support leg sidewall 44. Although this alternative embodiment shows the lifting lines 15 connected to the deck support leg top surfaces 41, the inventive methods of this invention can be practiced with the lifting lines 15 connected to other points present on the deck support legs 43 or on the buoyant substructure 20. Once the lifting lines 15 are connected to the deck support leg top surfaces 41 the buoyant substructure 20 can be ballasted down until the deck support leg top surfaces 41 are sufficiently submerged below the water surface to allow the self-floating deck structure 10 to be positioned over the submerged buoyant substructure 20. The self-floating deck structure 10 is positioned over the submerged buoyant substructure 20 such that each recessed cavity 11 of the self-floating deck structure 10 is aligned over the deck support leg top surfaces 41. The submerged buoyant substructure 20 is preferably suspended below the self-floating deck structure 10 by the lifting lines 15 connected to the lifting devices 16, as is illustrated in FIG. 12b. The lifting devices 16 retract the lifting lines 15 connected to the buoyant substructure thereby lifting the deck support leg top surfaces 41 into the recessed cavities 11 until the deck support leg top surfaces 41 mate with the recessed cavity ceiling surfaces 14 at a point above the water surface 35. After the deck support leg top surfaces 41 have contacted the recessed cavity ceiling surfaces 14, the two structures can be further connected by welding or by a mechanical device or plurality of mechanical devices.

[0315] After the deck support leg top surfaces 41 have mated with the recessed cavity ceiling surfaces 14 the buoyant substructure 20 can be deballasted to raise the self-floating deck structure 10 to a predetermined elevation above the water surface 35.

[0316] In an alternative embodiment of the method of the present invention, as is shown in FIG. 13, a self-floating deck structure 10 having a recessed cavity 11 is positioned adjacent to a floating buoyant substructure 20. A lifting line 15 is connected at one end to a lifting device 16 located on the self-floating deck structure 10 and is connected at the opposite end to the buoyant substructure 20. The buoyant substructure 20 is preferably ballasted down below the water surface 35 until it is totally submerged, and until the bottom surface 24 of the buoyant substructure 20 is resting on the seabed 30 in water sufficiently deep such that there is clearance between the bottom surface 12 of the self-floating deck structure 10 and the buoyant substructure top surface 21 when the self-floating deck structure 10 is positioned over the submerged buoyant substructure 20. The self-floating deck structure 10 is preferably positioned over the submerged buoyant substructure 20 so that the recessed cavity 11 of the self-floating deck structure 10 is aligned over the buoyant substructure top surface 21. The lifting device 16 retracts the lifting line 15 until the buoyant substructure top surface 21 is inserted into the recessed cavity 11 of the self-floating deck structure 10, and the buoyant substructure top surface 21 mates with the recessed cavity ceiling surface 14 at a point above the water surface 35.

[0317] In another embodiment of the methods of the present invention, as is shown in FIG. 14, the circumferential dimension of the upper circumferential edge 19 of the recessed cavity 11 is preferably smaller than the circumferential dimension of the lower circumferential edge 13 of the recessed cavity 11. The circumferential dimension of the upper circumferential edge 22 of the buoyant substructure 20 is preferably larger than the circumferential dimension of the upper circumferential edge 19 of the recessed cavity 11, and preferably smaller than the circumferential dimension of the lower circumferential edge 13 of the recessed cavity 11. The buoyant substructure top surface 21 and the buoyant substructure sidewall 25 adjacent to the buoyant substructure top surface 21 are preferably adapted to fit within the recessed cavity 11 of the self-floating deck structure 10, and are preferably sized so that the buoyant substructure sidewall 25 mates snugly with the recessed cavity sidewall 17 when the buoyant substructure top surface 21 is inserted into the recessed cavity 11. A lifting line 15 connected at one end to a lifting device 16 located on the self-floating deck structure 10 is lowered through the recessed cavity 11 present therein, and is connected at the opposite end to the buoyant substructure 20. The buoyant substructure 20 is preferably ballasted down below the water surface 35 until it is totally submerged in the water, and the buoyant substructure 20 is suspended from the self-floating deck structure,10 by the lifting line 15 connected to the lifting device 16. The self-floating deck structure 10 is preferably positioned over the buoyant substructure 20 so that the recessed cavity 11 is aligned over the buoyant substructure top surface 21. The lifting device 16 retracts the lifting line 15 connected to the buoyant substructure 20, thereby lifting the buoyant substructure top surface 21 into the recessed cavity 11 until the buoyant substructure sidewall 25 mates with the recessed cavity sidewall 17.

[0318] In another embodiment of the methods as shown in FIG. 15a, a plurality of floating vessels 55 are provided, each floating vessel having at least one line 38, said lines 38 being connected on one end to the vessel 55, the opposite end of each line being connected to the buoyant substructure 20 to prevent the buoyant substructure 20 from sinking to the seabed after the buoyant substructure 20 is ballasted below the water surface 35. As shown in FIG. 15a, two floating vessels 55 are depicted, however, it is recognized that the inventive method can be practiced with one or a plurality of floating vessels 55 (3, 4, 5, etc.).

[0319] In the embodiment shown in FIG. 15b, a plurality of buoyancy tanks 50 are connected by a line 38 to the buoyant substructure 20 to prevent the buoyant substructure 20 from sinking to the seabed after the buoyant substructure 20 is ballasted below the water surface 35. It is recognized that the inventive method is not restricted to two buoyancy tanks 50 as depicted but requires one or a plurality of buoyancy tanks 50 (3, 4, 5, etc.) be utilized.

[0320] It is recognized that the inventive methods of this invention can be practiced by ballasting the self-floating deck structure 10 down to facilitate the mating of the buoyant substructure top surface 21 or at least one deck support leg top surface 41 and at least one recessed cavity ceiling surface 14 of the self-floating deck structure 10 at a point above the water surface 35.

[0321] The inventive methods of this invention can be practiced by using lifting means 101 and a lifting device 16 located on the self-floating deck structure 10 to lift the buoyant substructure top surface 21 up into the recessed cavity 11. The lifting means 101 can include drill pipe, chain, cable, wire or rope. The lifting device 16 can include a drilling rig, winch, jack or crane. In this embodiment the buoyant substructure 20 is connected to a seabed 30 by mooring means 40 which can include for example mooring lines, cables, chains 40 or tension leg tendons 60. The buoyant substructure 20 is ballasted down below the water surface 35 until the buoyant substructure top surface 21 is sufficiently below the water surface 35 to allow a self-floating deck structure 10 to be positioned over the buoyant substructure top surface 21.

[0322] A self-floating deck structure 10 is positioned over the buoyant substructure 20 such that the recessed cavity 11 is aligned over the buoyant substructure top surface 21. A lifting means 101 is lowered from a lifting device 16 positioned on the self-floating deck structure 10 and is connected to the buoyant substructure 20. The lifting device 16 retracts the lifting means 101 lifting the buoyant substructure top surface 21 is inserted into the recessed cavity 11 in the self-floating deck structure 10 and mates with the ceiling surface 14 at a point above the water surface 35. The self-floating deck structure 10 and the buoyant substructure 20 can be further connected and the buoyant substructure 20 can be deballasted to raise the self-floating deck to a predetermined design elevation above the water surface 35.

[0323] If the buoyant substructure 20 is configured with a plurality deck support legs 43 a self-floating deck 10 provided with a plurality of recessed cavities 11 to accommodate the deck support leg top surfaces 41 of the deck support legs 43 is provided. The buoyant substructure is ballasted below the water surface 35 to a depth sufficient to allow a self-floating deck 10 to be positioned over the deck support leg top surfaces 41. Each recessed cavity 11 is aligned over a deck support leg top surface 41. The lifting means 101 is lowered from a lifting device 16 positioned on the self-floating deck structure 10 and is connected to the buoyant substructure 20. The lifting device 16 retracts the lifting means 101 lifting the buoyant substructure 20 until the deck support leg top surfaces 41 are inserted into the recessed cavities 11 and mate with the ceiling surfaces 14 in the recessed cavities 11 at a point above the water surface.

[0324] As shown in FIG. 16a, a buoyant frame 80 is provided. The buoyant frame 80 has a buoyant frame top surface 82 and a buoyant frame bottom surface 83. The buoyant frame 80 is further provided with an opening 81 that extends from the buoyant frame bottom surface 83 to the buoyant frame top surface 82. The opening 81 is sized and shaped to accommodate a buoyant substructure 20 positioned therein.

[0325] As shown in FIG. 16b, the buoyant frame 80 is connected to the seabed 30 by mooring means, examples of which include but are not limited to mooring lines, cables, chains (not shown), or tension leg tendons 60. A buoyant substructure 20 is positioned within the opening 81 in the buoyant frame 80. The buoyant substructure 20 has a buoyant substructure base member 45 that has perimetric dimensions greater than the perimetric dimensions of the opening 81 such that the buoyant substructure base member 45 of the buoyant substructure 20 cannot pass through the opening 81 in the submerged buoyant frame 80. The buoyant substructure base member 45 has a top face 46. The buoyant substructure 20 can optionally have a stopping means 65 positioned on the buoyant substructure sidewall 25 positioned above a buoyant frame top surface 82. The stopping means 65 is sized and shaped to prevent the buoyant substructure 20 from passing through the opening 81 in the buoyant frame 80. In the embodiment shown the stopping means 65 is a collar. The circumferential dimension of the collar is greater than the circumferential dimension of the opening 81 in the buoyant frame 80 such that the collar cannot pass through the opening 81, thus preventing the buoyant substructure 20 from disengaging from the buoyant frame 80. The stopping means 65 can be sized and shaped so that the stopping means 65 can support the buoyant substructure 20 when the stopping means 65 rests on the buoyant frame top surface 82. It is recognized that stopping means 65 can include padeyes, bearing pads or arms, struts, wedges or frames.

[0326] The buoyant substructure 20 is sized and shaped to fit within the opening 81 in the buoyant frame 80 and to allow movement in a vertical direction between the buoyant substructure 20 and the buoyant frame 80. The stopping means 65 and the buoyant substructure base member 45 of the buoyant substructure 20 limit the range of movement of the buoyant substructure 20 relative to the buoyant frame 80.

[0327] The buoyant substructure 20 can be positioned within the opening 81 in the buoyant frame 80 at the fabrication facility or other location and transported to the site installation. Alternatively, the buoyant substructure 20 can be positioned within the opening 81 in the buoyant frame 80 at the installation site. The buoyant frame 80 is submerged below the water surface 35 until it is positioned at a design depth. This can be achieved by increasing the tension in the mooring means or by adding ballast to the buoyant frame 80 or by a combination of increasing tension in the mooring means 40 and adding additional ballast to the buoyant frame 80.

[0328] A self-floating deck structure 10 with a recessed cavity 11 can be positioned adjacent to the buoyant substructure 20. A lifting line 15 connected to a lifting device 16 on the self-floating deck structure 10 can be connected to the buoyant substructure 20. The buoyant substructure 20 can be ballasted down in the water until the buoyant substructure top surface 21 is sufficiently below the water surface 35 such that the self-floating deck structure 10 can be positioned over the buoyant substructure top surface 21. The buoyant substructure 20 can be ballasted down until the buoyant substructure 20 is supported by the stopping means 65 resting on the buoyant frame top surface 82. Alternatively, as the buoyant substructure 20 is ballasted below the water surface 35, the lifting line 15 can support the buoyant substructure 20 and prevent it from sinking further than is required for the installation of the self-floating deck structure 10 onto the buoyant substructure 20.

[0329] The self-floating deck structure 10 is positioned over the submerged buoyant substructure 20 until the recessed cavity 11 of the self-floating deck structure 10 is aligned over the top surface 21 of the submerged buoyant substructure 20. The lifting device 16 is then activated to retract the lifting line 15 lifting the buoyant substructure 20 until the buoyant substructure top surface 21 contacts the recessed cavity ceiling surface 14 of the recessed cavity 11 of the self-floating deck structure 10 at a point above the water surface 35.

[0330] Alternatively, it is recognized that lifting means 101 and one or more lifting device 16 located on the self-floating deck structure 10 can be used to lift the buoyant substructure 20. In embodiment shown the buoyant substructure 20 is submerged below the water surface 35. The self-floating deck structure 10 is positioned over the submerged buoyant substructure 20. In the embodiment shown the lifting means 101 is drill pipe and the lifting device 16 is a drilling rig. It is recognized that the lifting means 101 can include drill pipe, chain, cable, wire or rope. It is further recognized that lifting device 16 can be a drilling rig, winch, jack or crane. The lifting means 101 is lowered from the lifting device 16 and is connected to the top surface 21 of buoyant substructure 20. The lifting means 101 is then lifted by activating the lifting device 16 to retract the lifting means 101 and lift the buoyant substructure 20 until the buoyant substructure top surface 21 mates with the recessed cavity ceiling surface 14 at a point above the water surface 35.

[0331] As shown in FIG. 16c, after the buoyant substructure top surface 21 has mated with the recessed cavity ceiling surface 14. The buoyant substructure 20 can be deballasted until the top face 46 of the buoyant substructure base member 45 mates with the buoyant frame bottom surface 83. The buoyant frame 80 provides horizontal stability to the buoyant substructure 20 while the buoyant substructure 20 and self-floating deck structure 10 are being raised by deballasting the buoyant substructure 20. The self-floating deck structure 10 is raised to a predetermined elevation above the water surface 35 by adjusting of the mooring means or by adjusting the ballast in the buoyant substructure 20 or buoyant frame 80. The submerged buoyant frame 80 can be connected to the buoyant substructure 20 by one or more methods, including grouting, welding and mechanical connectors.

[0332] As shown in FIG. 17a, in an alternative embodiment of the methods of the present invention a buoyant frame 80 with a plurality of openings 81 is provided. The buoyant frame 80 has a buoyant frame top surface 82 and a buoyant frame bottom surface 83. As shown in FIG. 17b, a buoyant substructure 20 with a plurality of deck support legs 43 is also provided. The deck support legs 43 extend upward from a top face 46 of a buoyant substructure base member 45. The deck support legs 43 are positioned within openings 81 in the buoyant frame 80. After the deck support legs 43 are positioned within the openings 81 in the buoyant frame 80, a stopping means 65 can be attached to the deck support leg sidewall 44 of one or more deck support legs 43. The stopping means 65 are sized and shaped to prevent the deck support legs 43 from passing through the openings 81 in the buoyant frame 80. In the embodiment shown the stopping means 65 is a collar. The circumferential dimension of the collar is greater than the circumferential dimension of the openings 81 in the buoyant frame 80 to prevent the deck support legs 43 from disengaging from the openings 81 in the buoyant frame 80. The stopping means 65 can be positioned on the deck support legs 43 to allow the deck support legs 43 to move up and down relative to the buoyant frame 80. The stopping means 65 can be sized and shaped so that it can support the buoyant substructure 20 when the stopping means 65 rests on the buoyant frame top surface 82.

[0333] The buoyant frame 80 and the buoyant substructure 20 are transported to an installation site. In the preferred embodiment the buoyant frame 80 and the buoyant substructure 20 are transported to the installation site as an engaged unit. However, it is recognized that the buoyant frame 80 and the buoyant substructure 20 can be transported separately and engaged at the site.

[0334] As shown in FIG. 18a, the buoyant frame 80 can be connected to the seabed 30 by mooring means 40, examples of which include but are not limited to mooring lines, cables, chains or tension leg tendons 60. The buoyant frame 80 is submerged by adding ballast to the buoyant frame 80 or by increasing the tension in the mooring means 40 or by a combination of both. Once the submerged buoyant frame 80 is positioned at the designed depth below the water surface 35 a self-floating deck structure 10 with more than one recessed cavity 11 can be positioned adjacent to the buoyant substructure 20. A plurality of lifting lines 15 from a plurality of lifting devices 16 on the self-floating deck structure 10 are connected to the top surfaces 41 of the deck support legs 43 of the buoyant substructure 20. The buoyant substructure 20 is then ballasted down until the top surfaces 41 of the deck support legs 43 are completely below the water surface 35. If stopping means 65 have been installed on the deck support leg sidewalls 44 the buoyant substructure 20 can be ballasted down until the stopping means 65 positioned on the deck support legs 43 rest on the buoyant frame top surface 82. Alternatively, the submerged buoyant substructure 20 can be supported by one or more lifting lines 15. The self-floating deck structure 10 is then positioned over the submerged buoyant substructure 20 and the recessed cavities 11 are aligned over the deck support leg top surfaces 41. In the embodiment shown, floating vessels 55 are used to position the self-floating deck structure 10.

[0335] In an embodiment shown in FIG. 18b, lifting means 101 is lowered from a lifting device 16 located on the self-floating deck structure 10. In the embodiment shown, the lifting means 101 is connected to the buoyant substructure base member 45, however, the lifting means 101 can be connected elsewhere on the buoyant substructure 20. The lifting device 16 retracts the lifting means 101 raising the buoyant substructure 20 until the deck support leg top surfaces 41 mate with the ceiling surfaces 14 of the recessed cavities 11 in the self-floating deck structure 10 at a point above the water surface. It is also recognized that one or more lifting lines 15 can be connected to one or more lifting devices 16 on the self-floating deck structure 10 and can be used to lift the buoyant substructure 20 instead of lifting means 110.

[0336] As shown in FIG. 18c, the buoyant substructure 20 can then be deballasted until the self-floating deck structure 10 is raised to a design elevation above the water surface 35, and the top face 46 of the buoyant substructure base member 45 mates with the buoyant frame bottom surface 83. The buoyant substructure 20 can be connected to the buoyant frame 80 by welding, mechanical connection, or grouting or a combination thereof. The buoyant substructure 20 and the self-floating deck structure 10 can be further connected by welding or mechanical connectors or a combination on welding and mechanical connectors.

[0337] In an alternative embodiment of the methods of the present invention as shown in FIG. 19a a buoyant substructure 20 is connected to a base structure 90 by at least one connecting means which can include mechanical connectors (not shown) or one or more tension member 91 such as a cable, chain, or pipe. The base structure 90 has a base structure top surface 92, a base structure bottom surface 93 and base structure opening 94 extending from the base structure top surface 92 to the base structure bottom surface 93. The base structure 90 can be buoyant but can also be fabricated such that it is not buoyant. It is also recognized that the base structure bottom surface 93 can extend across said base structure opening 94 creating a closed end. The base structure opening 94 is sized and shaped to accommodate a buoyant substructure 20. The base structure 90 also has a hollow tube 96 extending upward from the base structure top surface 92. In the embodiment shown, the tube 96 is cylindrical however it is recognized that other shapes are also suitable. The hollow tube having the same shape and internal perimetric dimension as the base structure opening. The hollow tube 96 being sized and shaped such that the buoyant substructure 20 can fit within the tube 96 and move relative to the tube 96. The buoyant substructure 20 is positioned at least partially within the tube 96 and is connected to the base structure 90 by connecting means. In the embodiment shown the connecting means is a tension member 91. The base structure 90 and buoyant substructure 20 can be transported to an installation site.

[0338] As shown in FIG. 19b the base structure 90 is positioned on the seabed 30 by adding ballast to either the buoyant substructure 20 or the base structure 90 or optionally both the buoyant substructure 20 and the base structure 90. The base structure 90 can be affixed to the seabed 30 by gravity, ballast, or mechanical connectors such as piling depending on design considerations. A self-floating deck structure 10 is positioned adjacent to the buoyant substructure 20. At least one lifting line 15 connected to at least one lifting device 16 on the self-floating deck structure 10 is connected to the buoyant substructure top surface 21. The buoyant substructure 20 is ballasted down below the water surface 35 to a depth sufficient to allow a self-floating deck structure 10 to be positioned over a top surface 21 of the submerged buoyant substructure 20. As shown in FIG. 19c the buoyant substructure 20 is ballasted below the water surface 35 until the buoyant substructure 20 rests on the base structure bottom surface 93. As shown in FIG. 19d a self-floating deck structure 10 can be positioned over the submerged buoyant substructure 20. As shown in FIG. 19e the lifting device 16 is activated and retracts the lifting line 15 until the top surface 21 of the buoyant substructure 20 is inserted into the recessed cavity 11 of the self-floating desk structure 10, and the top surface 21 mates with the ceiling surface 14 of the recessed cavity 11. As shown in FIG. 19f the self-floating deck structure 10 can be raised to a predetermined elevation above the water surface 35 by deballasting the buoyant substructure 20. After the self-floating deck structure 10 is raised to the predetermined elevation the buoyant substructure 20 can be connected to the hollow tube 96 by one or more connecting means 97 such as grouting, mechanical connectors or welding as is known by those skilled in the art.

[0339] In an alternative embodiment of the methods of the present invention as shown in FIG. 20a, the buoyant frame 80 further comprises a hollow tube 96 that extends upward from the buoyant frame top surface 82 in alignment with the opening 81 in the buoyant frame. The hollow tube 96 and the opening 81 are sized and shaped such that the buoyant substructure 20 can fit within the opening 81 and hollow tube 96 and move relative to the opening 81 and the hollow tube 96. The buoyant substructure 20 is positioned at least partially within said hollow tube 96. The buoyant frame 80 is connected to the seabed 30 by mooring means 40, examples of which include wire, cable, chain, pipe and tension leg tendons. The buoyant frame 80 is submerged below the water surface 35 at a predetermined design depth by adding ballast to the buoyant frame 80 or by adjusting the mooring means 40. In the present embodiment the mooring means 40 are tension leg tendons 60. A self-floating deck structure 10 is positioned adjacent to the buoyant substructure 20. At least one lifting line 15 connected to a lifting device 16 on the self-floating deck structure 10 is connected to the buoyant substructure top surface 21. The top surface 21 of the buoyant substructure 20 is positioned below the water surface 35 by adjusting the amount of ballast in the buoyant substructure 20. As shown in FIG. 20b a self-floating deck structure 10 is positioned over the buoyant substructure 20. As shown in FIG. 20c the lifting device 16 is activated to retract the lifting line 15 until the top surface 21 of the buoyant substructure 20 is inserted into the recessed cavity 11 of the self-floating deck structure 10, and the top surface 21 of the buoyant substructure 20 mates with the ceiling surface 14 of the recessed cavity 11 at a point above the water surface.

[0340] In an alternative embodiment, lifting means 101 and one or more lifting devices 16 located on the self-floating deck 10 can be used to lift the buoyant substructure 20. The buoyant substructure 20 is ballasted down below the water surface 35 to a depth sufficient to allow a self-floating deck structure 10 to be positioned over the top surface 21 of the buoyant substructure 20. A self-floating deck structure 10 is positioned over the buoyant substructure until the recessed cavity 11 is aligned over the top surface 21 of the buoyant substructure 20. The lifting means 101 can be lowered from a lifting device 16 located on the self-floating deck structure 10 and is connected to the buoyant substructure 20 until the top surface 21 is inserted into the recessed cavity 11 and mates with the surface 14 of the recessed cavity 11 at a point above the water surface. The lifting means 101 is then raised by a lifting device 16 raising the buoyant substructure 20. In the embodiment shown the lifting means 101 is drill pipe and the lifting device 16 is a drilling rig.

[0341] As shown in FIG. 20d the buoyant substructure 20 can be deballasted to raise the self-floating deck structure 10 to a predetermined design elevation above the water surface 35. The buoyant substructure 20 is then connected to the hollow tube 96 by connecting means 97 examples of which include welding, mechanical connectors or grouting.

[0342] In an alternative embodiment as shown in FIG. 21a the self-floating deck structure 10 has at least two hulls 5 extending from the bottom surface 12 of the self-floating deck structure 10. The hulls 5 provide buoyancy for the self-floating deck structure 10 and are sized and shaped such that the bottom surface 12 is positioned above the water surface 35. The hulls 5 are further sized and shaped to allow the self-floating deck structure 10 to be positioned over the buoyant substructure top surface 21 of a buoyant substructure 20 and have sufficient clearance as is known to those skilled in the art such that the bottom surface 12 and the buoyant substructure top surface 21 do not collide when the self-floating deck structure 10 is positioned over the buoyant substructure 20. The self-floating deck structure 10 is positioned over the buoyant substructure 20. It is preferable but not required that the buoyant substructure 20 has been installed and connected to the seabed by mooring means 40 prior to the commencement of the self-floating deck structure 10 installation. At least one lifting means 101 connected to at least one lifting device 16 located on the self-floating deck structure 10 is lowered and connected to the buoyant substructure 20. As shown in FIG. 21b at least one lifting device 16 is activated to retract the lifting means 101 lifting the buoyant substructure 20 until the buoyant substructure top surface 21 mates with the bottom surface 12 of the self-floating deck structure 10. The self-floating deck structure 10 can be connected to the buoyant substructure 20 by welding or one or more mechanical connectors. The self-floating deck structure 10 is raised to a predetermined elevation above the water surface 35 by adjusting the mooring means 40 or by adjusting the ballast in the buoyant substructure 20.

[0343] In an alternative embodiment as shown in FIG. 22a the self-floating deck structure 10 has at least two hulls 5 extending from the bottom surface 12 of the self-floating deck structure 10. The hulls 5 provide buoyancy for the self-floating deck structure 10 and are sized and shaped such that the bottom surface 12 is positioned above the water surface 35. The hulls 5 are further sized and shaped to allow the self-floating deck structure 10 to be positioned over a buoyant substructure 20 that is provided with a plurality of deck support legs 43 and have sufficient clearance as is known to those skilled in the art such that the bottom surface 12 and the deck support leg top surfaces 41 do not collide when the self-floating deck structure 10 is positioned over the buoyant substructure 20. The self-floating deck structure 10 is positioned over the deck support leg top surfaces 41 of the buoyant substructure 20. It is preferable but not required that the buoyant substructure 20 has been installed and connected to the seabed by mooring means 40 prior to the commencement of the self-floating deck structure 10 installation. At least one lifting means 101 connected to at least one lifting device 16 located on the self-floating deck structure 10 is lowered and connected to the buoyant substructure 20. As shown in FIG. 22b at least one lifting device 16 is activated to retract the lifting means 101 lifting the buoyant substructure 20 until the deck support leg top surfaces 41 of buoyant substructure 20 mate with the bottom surface 12 of the self-floating deck structure 10. The self-floating deck structure 10 can be connected to the buoyant substructure by welding or one or more mechanical connectors. The self-floating deck structure 10 is raised to a predetermined elevation above the water surface 35 by adjusting the mooring means 40 or by adjusting the ballast in the buoyant substructure 20.

[0344] The dimensions of these structures can vary widely as known by those with skill in the art. The materials used to fabricate these structures can vary but are typically metal or composite materials.

[0345] Certain preferred embodiments of the methods of the present invention have been illustrated and described herein. Because many varying and differing embodiments of the methods of the present invention may be made within the scope of the inventive concepts herein taught, and because many variations, modifications and substitutions of that which has been illustrated and described herein, such as by adding, combining, or by subdividing parts or steps, or by substituting equivalents, may be made to the embodiments of the present invention herein detailed, it is to be understood that the details of the present invention set forth herein are to be interpreted as illustrative, and not in a limiting sense. It is intended, therefore, that all of those modifications, variations and substitutions within the scope and spirit of the present invention as illustrated, described and claimed herein, and that the claims that follow be interpreted as broadly as possible. 

What is claimed is:
 1. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each line to the buoyant substructure; (e) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from the self-floating deck structure by at least one lifting line connected to at least one lifting device; (f) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (g) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 2. The method according to claim 1 wherein the lifting line is a chain, wire cable, synthetic cable, or a rope.
 3. The method according to claim 1 wherein the lifting device is a winch, a jack, a drilling rig or a crane.
 4. The method according to claim 1 wherein the lower circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 5. The method according to claim 1 wherein the upper circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 6. The method according to claim 1 wherein one or more lines separate from the lifting line connected to the lifting device suspends the buoyant substructure from the self-floating deck structure.
 7. The method according to claim 1 wherein the upper circumferential edge of the buoyant substructure has a rounded shape.
 8. The method according to claim 1 wherein the circumferential dimension of the upper circumferential edge of at least one recessed cavity of the self-floating deck structure is smaller than the circumferential dimension of the lower circumferential edge of the same recessed cavity causing the recessed cavity sidewall to taper inward as it progresses from said lower circumferential edge of the recessed cavity towards said upper circumferential edge of the recessed cavity.
 9. The method according to claim 8 wherein the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface are adapted to fit within the recessed cavity of the floating deck structure and are sized so that the circumferential dimension of the upper circumferential edge of the buoyant substructure is smaller than the circumferential dimension of the buoyant substructure sidewall.
 10. The method according to claim 1 wherein the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface are adapted to fit within the recessed cavity of the floating deck structure and are sized so that the circumferential dimension of the upper circumferential edge of the buoyant substructure is smaller than the circumferential dimension of the buoyant substructure sidewall.
 11. The method according to claim 1 wherein compressed air or gas is injected into at least one recessed cavity of the self-floating deck structure until a portion or all of the water within said recessed cavity is expelled.
 12. The method according to claim 1 wherein a plurality of lifting devices and lifting lines are utilized to lift the buoyant substructure top surface into the recessed cavity of the self-floating deck structure.
 13. The method according to claim 1 wherein at least one buoyancy tank is provided, each buoyancy tank having at least one line having one end connected to said buoyancy tank and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface.
 14. The method according to claim 1 wherein at least one floating vessel is provided, each floating vessel having at least one line having one end connected to said floating vessel and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface.
 15. The method according to claim 1 wherein the self-floating deck structure is ballasted down to facilitate the mating of the buoyant substructure top surface and the recessed cavity ceiling surface of the self-floating deck structure.
 16. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming a circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity present in the self-floating deck structure; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) connecting at least one lifting line connected to at least one lifting device located on the self-floating deck structure to the buoyant substructure; (e) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from the self-floating deck structure by at least one lifting line connected to at least one lifting device; (f) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface present on the buoyant substructure; (g) activating each lifting device to retract each connected lifting line and lift the buoyant substructure up until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface; (h) connecting the self-floating deck structure to the buoyant substructure by welding or by a plurality of mechanical devices; and (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 17. The method according to claim 16 wherein the lifting line is a chain, wire cable, synthetic cable, or a rope.
 18. The method according to claim 16 wherein the lifting device is a winch, a jack, a drilling rig or a crane.
 19. The method according to claim 16 wherein the lower circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 20. The method according to claim 16 wherein the upper circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 21. The method according to claim 16 wherein one or more lines separate from the lifting lines connected to the lifting devices suspends the buoyant substructure from the self-floating deck structure.
 22. The method according to claim 16 wherein the upper circumferential edge of at least one deck support leg has a rounded shape.
 23. The method according to claim 16 wherein the circumferential dimension of the upper circumferential edge of at least one recessed cavity of the self-floating deck structure is smaller than the circumferential dimension of the lower circumferential edge of the same recessed cavity causing the recessed cavity sidewall to taper inward as it progresses from said lower circumferential edge of the recessed cavity towards said upper circumferential edge of the recessed cavity.
 24. The method according to claim 23 wherein the deck support leg top surface and the deck support leg sidewall adjacent to the deck support leg top surface are adapted to fit within a recessed cavity of the self-floating deck structure and are sized so that circumferential dimension of the circumferential edge of the deck support leg is smaller than the circumferential dimension of the deck support leg sidewall.
 25. The method according to claim 16 wherein the deck support leg top surface and the deck support leg sidewall adjacent to the deck support leg top surface are adapted to fit within a recessed cavity of the self-floating deck structure and are sized so that circumferential dimension of the circumferential edge of the deck support leg is smaller than the circumferential dimension of the deck support leg sidewall.
 26. The method according to claim 16 wherein compressed air or gas is injected into at least one recessed cavity of the self-floating deck structure until a portion or all of the water within said recessed cavity is expelled.
 27. The method according to claim 16 wherein at least one buoyancy tank is provided, each buoyancy tank having at least one line having one end connected to said buoyancy tank and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface.
 28. The method according to claim 16 wherein at least one floating vessel is provided, each floating vessel having at least one line having one end connected to said floating vessel and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface.
 29. The method according claim 16 wherein the self-floating deck structure is ballasted down to facilitate the mating of at least one deck support leg top surface and at least one recessed cavity ceiling surface.
 30. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure, said self-floating deck structure having a bottom surface and a recessed cavity extending upward from the bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming an upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (c) positioning the self-floating deck structure adjacent to said buoyant substructure and connecting at least one lifting line connected to at least one lifting device located on the self-floating deck structure to the buoyant substructure; (d) ballasting the buoyant substructure below the water surface until the buoyant substructure bottom surface rests upon a seabed present in the water deep enough so that the buoyant substructure top surface is below the bottom surface of the self-floating deck structure; (e) positioning the self-floating deck structure over the submerged buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (f) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity of the self-floating deck structure until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (g) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (h) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface suitable for towing the connected self-floating deck structure and buoyant substructure to a final installation location.
 31. The method according to claim 30 wherein the lifting line is a chain, wire cable, synthetic cable, or a rope.
 32. The method according to claim 30 wherein the lifting device is a winch, a jack, a drilling rig or a crane.
 33. The method according to claim 30 wherein the lower circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 34. The method according to claim 30 wherein the upper circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 35. The method according to claim 30 wherein the upper circumferential edge of the buoyant substructure has a rounded shape.
 36. The method according to claim 30 wherein the circumferential dimension of the upper circumferential edge of at least one recessed cavity of the self-floating deck structure is smaller than the circumferential dimension of the lower circumferential edge of the same recessed cavity causing the recessed cavity sidewall to taper inward as it progresses from said lower circumferential edge of the recessed cavity towards said upper circumferential edge of the recessed cavity.
 37. The method according to claim 36 wherein the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface are adapted to fit within the recessed cavity of the floating deck structure and are sized so that the circumferential dimension of the upper circumferential edge of the buoyant substructure is smaller than the circumferential dimension of the buoyant substructure sidewall.
 38. The method according to claim 30 wherein the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface are adapted to fit within the recessed cavity of the floating deck structure and are sized so that the circumferential dimension of the upper circumferential edge of the buoyant substructure is smaller than the circumferential dimension of the buoyant substructure sidewall.
 39. The method according to claim 30 wherein compressed air or gas is injected into at least one recessed cavity of the self-floating deck structure until a portion of or all the water within said recessed cavity is expelled.
 40. The method according to claim 30 wherein a plurality of lifting devices and lifting lines lift the buoyant substructure top surface into the recessed cavity of the self-floating deck structure.
 41. The method according to claim 30 wherein the self-floating deck structure is ballasted down to facilitate the mating of the buoyant substructure top surface and the recessed cavity ceiling surface of the self-floating deck structure.
 42. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming an upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure that has a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming at least one circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity of the self-floating deck structure; (c) positioning the self-floating deck structure adjacent to said buoyant substructure and connecting at least one lifting line connected to at least one lifting device present on the self-floating deck structure to the buoyant substructure; (d) ballasting the buoyant substructure below the water surface until the buoyant substructure bottom surface rests upon a seabed present in the water deep enough so that each deck support leg top surface is positioned below the bottom surface of the self-floating deck structure; (e) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure is aligned over a deck support leg top surface of the buoyant substructure; (f) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure up until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with the recessed cavity ceiling surface at a point above the water surface; (g) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (h) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 43. The method according to claim 42 wherein the lifting line is a chain, wire cable, synthetic cable, or a rope.
 44. The method according to claim 42 wherein the lifting device is a winch, a jack, a drilling rig or a crane.
 45. The method according to claim 42 wherein the lower circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 46. The method according to claim 42 wherein the upper circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 47. The method according to claim 42 wherein the upper circumferential edge of at least one deck support leg has a rounded shape.
 48. The method according to claim 42 wherein the circumferential dimension of the upper circumferential edge of at least one recessed cavity of the self-floating deck structure is smaller than the circumferential dimension of the lower circumferential edge of the same recessed cavity causing the recessed cavity sidewall to taper inward as it progresses from said lower circumferential edge of the recessed cavity towards said upper circumferential edge of the recessed cavity.
 49. The method according to claim 48 wherein the deck support leg top surface and the deck support leg sidewall adjacent to the deck support left top surface are adapted to fit within a recessed cavity of the self-floating deck structure and are sized so that circumferential dimension of the circumferential edge of the deck support leg is smaller than the circumferential dimension of the deck support leg sidewall.
 50. The method according to claim 42 wherein the deck support leg top surface and the deck support leg sidewall adjacent to the deck support left top surface are adapted to fit within a recessed cavity of the self-floating deck structure and are sized so that circumferential dimension of the circumferential edge of the deck support leg is smaller than the circumferential dimension of the deck support leg sidewall.
 51. The method according to claim 42 wherein compressed air or gas is injected into at least one recessed cavity of the self-floating deck structure until a portion of or all the water within said recessed cavity is expelled.
 52. The method according claim 42 wherein the self-floating deck structure is ballasted down to facilitate the mating of at least one deck support leg top surface and at least one recessed cavity ceiling surface.
 53. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure with a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an opened end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and said buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming at least one upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) providing at least one line that is connected to the self-floating deck structure; (e) connecting each line to the buoyant substructure; (f) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from the self-floating deck structure by at least one line; (g) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (h) raising the buoyant substructure top surface up into the recessed cavity by adjusting the buoyancy of the buoyant substructure until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (i) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical device; and (j) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 54. The method according to claim 53 wherein the line is a chain, wire cable, synthetic cable, or a rope.
 55. The method according to claim 53 wherein the lower circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 56. The method according to claim 53 wherein the upper circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 57. The method according to claim 53 wherein the upper circumferential edge of the buoyant substructure has a rounded shape.
 58. The method according to claim 53 wherein the circumferential dimension of the upper circumferential edge of at least one recessed cavity of the self-floating deck structure is smaller than the circumferential dimension of the lower circumferential edge of the same recessed cavity causing the recessed cavity sidewall to taper inward as it progresses from said lower circumferential edge of the recessed cavity towards said upper circumferential edge of the recessed cavity.
 59. The method according to claim 58 wherein the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface are adapted to fit within the recessed cavity of the floating deck structure and are sized so that the circumferential dimension of the upper circumferential edge of the buoyant substructure is smaller than the circumferential dimension of the buoyant substructure sidewall.
 60. The method according to claim 53 wherein the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface are adapted to fit within the recessed cavity of the floating deck structure and are sized so that the circumferential dimension of the upper circumferential edge of the buoyant substructure is smaller than the circumferential dimension of the buoyant substructure sidewall.
 61. The method according to claim 53 wherein compressed air or gas is injected into at least one recessed cavity of the self-floating deck structure until a portion of or all the water within said recessed cavity is expelled.
 62. The method according to claim 53 wherein at least one buoyancy tank is provided, each buoyancy tank having at least one line having one end connected to said buoyancy tank and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface.
 63. The method according to claim 53 wherein at least one floating vessel is provided, each floating vessel having at least one line having one end connected to said floating vessel and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed as the buoyant substructure is ballasted below the water surface.
 64. The method according to claim 53 wherein the self-floating deck structure is ballasted down to facilitate the mating of the buoyant substructure top surface and the recessed cavity ceiling surface of the self-floating deck structure.
 65. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above the water surface, the intersection of the recessed cavity sidewalls and the recessed cavity ceiling surfaces forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewalls and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure bottom surface, each deck support leg having a deck support leg top surface and a deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming at least one circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity of the self-floating deck structure; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) providing at least one line that is connected to said self-floating deck structure; (e) connecting each line to the buoyant substructure; (f) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg of the buoyant substructure is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from at least one line connected to the self-floating deck structure; (g) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface of the buoyant substructure; (h) raising the buoyant substructure up by adjusting the buoyancy of the buoyant substructure until each of deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface; (i) connecting the self-floating deck structure to the buoyant substructure of the self-floating deck structure by welding or by one or more mechanical devices; and (j) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 66. The method according to claim 65 wherein the line is a chain, wire cable, synthetic cable, or a rope.
 67. The method according to claim 65 wherein the lower circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 68. The method according to claim 65 wherein the upper circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 69. The method according to claim 65 wherein the upper circumferential edge of at least one deck support leg has a rounded shape.
 70. The method according to claim 65 wherein the circumferential dimension of the upper circumferential edge of at least one recessed cavity of the self-floating deck structure is smaller than the circumferential dimension of the lower circumferential edge of the same recessed cavity causing the recessed cavity sidewall to taper inward as it progresses from said lower circumferential edge of the recessed cavity towards said upper circumferential edge of the recessed cavity.
 71. The method according to claim 70 wherein the deck support leg top surface and the deck support leg sidewall adjacent to the deck support left top surface are adapted to fit within a recessed cavity of the self-floating deck structure and are sized so that circumferential dimension of the circumferential edge of the deck support leg is smaller than the circumferential dimension of the deck support leg sidewall.
 72. The method according to claim 65 wherein the deck support leg top surface and the deck support leg sidewall adjacent to the deck support left top surface are adapted to fit within a recessed cavity of the self-floating deck structure and are sized so that circumferential dimension of the circumferential edge of the deck support leg is smaller than the circumferential dimension of the deck support leg sidewall.
 73. The method according to claim 65 wherein compressed air or gas is injected into at least one recessed cavity of the self-floating deck structure until a portion or all of the water within said recessed cavity is expelled.
 74. The method according to claim 65 wherein at least one buoyancy tank is provided, each buoyancy tank having at least one line having one end connected to said buoyancy tank and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface.
 75. The method according to claim 65 wherein at least one floating vessel is provided, each floating vessel having at least one line having one end connected to said floating vessel and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed as the buoyant substructure is ballasted below the water surface.
 76. The method according claim 65 wherein the self-floating deck structure is ballasted down to facilitate the mating of at least one deck support leg top surface and at least one recessed cavity ceiling surface.
 77. A method of installing a self-floating deck structure on to a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure, said self-floating deck structure having a bottom surface and a recessed cavity extending upward from the bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above the water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming at least one upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (c) positioning the self-floating deck structure adjacent to said buoyant substructure that has been ballasted below the water surface so that the buoyant substructure bottom surface rests on a seabed present in the water deep enough such that the buoyant substructure top surface is below the bottom surface of the self-floating deck structure; (d) positioning the self-floating deck structure over the submerged buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (e) raising the buoyant substructure top surface up into the recessed cavity of the self-floating deck structure by adjusting the buoyancy of the buoyant substructure until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (f) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (g) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface suitable for towing the connected self-floating deck structure and buoyant substructure to a final installation location.
 78. The method according to claim 77 wherein the lower circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 79. The method according to claim 77 wherein the upper circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 80. The method according to claim 77 wherein the upper circumferential edge of the buoyant substructure has a rounded shape.
 81. The method according to claim 77 wherein the circumferential dimension of the upper circumferential edge of at least one recessed cavity of the self-floating deck structure is smaller than the circumferential dimension of the lower circumferential edge of the same recessed cavity causing the recessed cavity sidewall to taper inward as it progresses from said lower circumferential edge of the recessed cavity towards said upper circumferential edge of the recessed cavity.
 82. The method according to claim 81 wherein the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface are adapted to fit within the recessed cavity of the floating deck structure and are sized so that the circumferential dimension of the upper circumferential edge of the buoyant substructure is smaller than the circumferential dimension of the buoyant substructure sidewall.
 83. The method according to claim 77 wherein the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface are adapted to fit within the recessed cavity of the floating deck structure and are sized so that the circumferential dimension of the upper circumferential edge of the buoyant substructure is smaller than the circumferential dimension of the buoyant substructure sidewall.
 84. The method according to claim 77 wherein compressed air or gas is injected into at least one recessed cavity of the self-floating deck structure until a portion of or all the water within said recessed cavity is expelled.
 85. The method according to claim 77 wherein the self-floating deck structure is ballasted down to facilitate the mating of the buoyant substructure top surface and the recessed cavity ceiling surface of the self-floating deck structure.
 86. A method for installing a self-floating deck structure on to a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above the water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming at least one circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity of the self-floating deck structure; (c) ballasting the buoyant substructure below the water surface until the buoyant substructure bottom surface rests on a seabed present in the water deep enough so that each deck support leg top surface is below the bottom surface of the self-floating deck structure; (d) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface of the buoyant substructure; (e) raising the buoyant substructure up by adjusting the buoyancy of the buoyant substructure until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface; (f) connecting the self-floating deck structure to the buoyant substructure of the self-floating deck structure by welding or by one or more mechanical devices; and (g) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 87. The method according to claim 86 wherein the lower circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 88. The method according to claim 86 wherein the upper circumferential edge of at least one recessed cavity in the self-floating deck structure has a rounded shape.
 89. The method according to claim 86 wherein the upper circumferential edge of at least one deck support leg has a rounded shape.
 90. The method according to claim 86 wherein the circumferential dimension of the upper circumferential edge of at least one recessed cavity of the self-floating deck structure is smaller than the circumferential dimension of the lower circumferential edge of the same recessed cavity causing the recessed cavity sidewall to taper inward as it progresses from said lower circumferential edge of the recessed cavity towards said upper circumferential edge of the recessed cavity.
 91. The method according to claim 90 wherein the deck support leg top surface and the deck support leg sidewall adjacent to the deck support left top surface are adapted to fit within a recessed cavity of the self-floating deck structure and is sized so that circumferential dimension of the circumferential edge of the deck support leg is smaller than the circumferential dimension of the deck support leg sidewall.
 92. The method according to claim 86 wherein the deck support leg top surface and the deck support leg sidewall adjacent to the deck support left top surface are adapted to fit within a recessed cavity of the self-floating deck structure and is sized so that circumferential dimension of the circumferential edge of the deck support leg is smaller than the circumferential dimension of the deck support leg sidewall.
 93. The method according to claim 86 wherein compressed air or gas is injected into at least one recessed cavity of the self-floating deck structure until a portion of or all the water within said recessed cavity is expelled.
 94. The method according claim 86 wherein the self-floating deck structure is ballasted down to facilitate the mating of at least one deck support leg top surface and at least one recessed cavity ceiling surface.
 95. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure with a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, a recessed cavity ceiling surface at least one recessed cavity sidewall, said recessed cavity ceiling surface being positioned above the water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity, the dimension of the upper circumferential edge of the recessed cavity being smaller than the dimension of the lower circumferential edge of the recessed cavity causing the recessed cavity sidewall to taper inward as it progresses from said lower circumferential edge of the recessed cavity towards said upper circumferential edge of the recessed cavity; (b) providing a buoyant substructure that is capable of being fully submerged below a water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming at least one upper circumferential edge of the buoyant substructure, the circumferential dimension of the buoyant substructure top surface being larger than the circumferential dimension of the recessed cavity ceiling surface but smaller than the circumferential dimension of the lower circumferential edge of the recessed cavity, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted to fit within the recessed cavity of the self-floating deck structure, and being sized so that the buoyant substructure sidewall mates snugly with the recessed cavity sidewall when the buoyant substructure top surface is inserted in the recessed cavity; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each line to the buoyant substructure; (e) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from the self-floating deck structure by at least one lifting line connected to at least one lifting device; (f) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (g) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity until the buoyant substructure sidewall mates with the recessed cavity sidewall; (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 96. A method of installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure with a bottom surface and at least one recessed cavity extending upward from said bottom surface of the self-floating deck structure, each recessed cavity comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each recessed cavity ceiling surface being positioned above the water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming at least one circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity of the self-floating deck structure; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure; (e) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from the self-floating deck structure by at least one lifting line connected to at least one lifting device; (f) positioning the self-floating deck structure over the buoyant substructure so that at least one recessed cavity of the self-floating deck structure is aligned over a plurality of deck support leg top surfaces of the buoyant substructure; (g) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure up until a plurality of deck support leg top surfaces are inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface; (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 97. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure; (e) providing at least one buoyancy tank, each buoyancy tank having at least one line having one end connected to said buoyancy tank and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface; (f) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from at least one buoyancy tank by at least one line connected to at least one buoyancy tank; (g) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (h) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (i) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (j) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 98. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) providing at least one buoyancy tank, each buoyancy tank having at least one line having one end connected to said buoyancy tank and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface; (e) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from at least one buoyancy tank by at least one line connected to at least one buoyancy tank; (f) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (g) raising the buoyant substructure top surface up into the recessed cavity by adjusting the buoyancy of the buoyant substructure until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 99. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure; (e) providing at least one floating vessel, each floating vessel having at least one line having one end connected to said floating vessel and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface; (f) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from at least one floating vessel by at least one line connected to at least one floating vessel; (g) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (h) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (i) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (j) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 100. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) providing at least one floating vessel, each floating vessel having at least one line having one end connected to said floating vessel and an opposite end connected to the buoyant substructure to prevent said buoyant substructure from sinking to the seabed after the buoyant substructure is ballasted below the water surface; (e) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure and the buoyant substructure is suspended from at least one floating vessel by at least one line connected to at least one floating vessel; (f) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (g) raising the buoyant substructure top surface up into the recessed cavity by adjusting the buoyancy of the buoyant substructure until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 101. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure; (e) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (f) lowering lifting means from one or more lifting devices positioned on said self-floating deck structure and connecting said lifting means to said buoyant substructure; (g) activating the lifting device to retract the lifting means and lift the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (h) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 102. The method according to claim 101 wherein said lifting means is drill pipe, chain, cable, wire or rope.
 103. The method according to claim 101 wherein said lifting device is a drilling rig, winch, jack or crane.
 104. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming a circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity present in the self-floating deck structure; (c) positioning said self-floating deck structure adjacent to said buoyant substructure; (d) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg is below the bottom surface of the self-floating deck structure; (e) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface present on the buoyant substructure; (f) lowering lifting means from one or more lifting device positioned on said self-floating deck structure and connecting said lifting means to said buoyant substructure; (g) activating the lifting device to retract the lifting means and lift the buoyant substructure up until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface; (h) connecting the self-floating deck structure to the buoyant substructure by welding or by a plurality of mechanical devices; and (i) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 105. The method according to claim 104 wherein said lifting means is drill pipe, chain, cable, wire or rope.
 106. The method according to claim 104 wherein said lifting is a drilling rig, winch, jack or crane.
 107. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant frame that is capable of being fully submerged below the water surface, said buoyant frame having a buoyant frame top surface and a buoyant frame bottom surface, said buoyant frame further having an opening extending through said buoyant frame from said buoyant frame top surface to said buoyant frame bottom surface, said opening being sized and shaped to allow a buoyant substructure to be positioned within said opening; (c) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface, said buoyant substructure further having a buoyant substructure base member that has perimetric dimensions greater than the perimetric dimensions of the opening in the buoyant frame, said buoyant substructure base member having a top face, said buoyant substructure having at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (d) positioning said buoyant substructure within said opening in said buoyant frame; (e) connecting said buoyant frame to a seabed by mooring means; (f) submerging said buoyant frame below the water surface at a predetermined design depth; (g) positioning said self-floating deck structure adjacent to said buoyant substructure; (h) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure; (i) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure; (j) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (k) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (l) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (m) deballasting the buoyant substructure until the top face of the buoyant substructure base member mates with the buoyant frame bottom surface; (n) connecting said buoyant frame to said buoyant substructure by welding or by one or more mechanical device; (o) raising the self-floating deck structure to a predetermined elevation above the water surface by adjusting said mooring means or deballasting said buoyant substructure or said buoyant frame.
 108. The method according to claim 107 wherein the lifting line is a chain, cable, wire or rope.
 109. The method according to claim 107 wherein the lifting device is a drilling rig, winch, jack or crane.
 110. The method according to claim 107 wherein said buoyant substructure is suspended from the self-floating deck structure by at least one lifting line connected to at least one lifting device when said buoyant substructure is ballasted below said water surface.
 111. The method according to claim 107 wherein said buoyant substructure is suspended from the self-floating deck structure by at least one chain, cable, wire or rope when said buoyant substructure is ballasted below said water surface.
 112. The method according to claim 107 wherein a stopping means is positioned on said buoyant substructure sidewall, said stopping means being sized and shaped such that said stopping means prevents said buoyant substructure from passing through said opening in said buoyant frame.
 113. The method according to claim 112 wherein said stopping means is sized and shaped to support the submerged buoyant substructure when said stopping means rests on the buoyant frame top surface.
 114. The method according to claim 113 wherein said buoyant substructure is ballasted down below said water surface until said stopping means rests on said buoyant frame top surface.
 115. The method according to claim 112 wherein said stopping means is a collar, the circumferential dimension of said collar being greater than the circumferential dimension of the opening in the buoyant frame.
 116. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant frame that is capable of being fully submerged below the water surface, said buoyant frame having a buoyant frame top surface and a buoyant frame bottom surface, said buoyant frame further having an opening extending through said buoyant frame from said buoyant frame top surface to said buoyant frame bottom surface, said opening being sized and shaped to allow a buoyant substructure to be positioned within said opening; (c) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface, said buoyant substructure further having a buoyant substructure base member that has perimetric dimensions greater than the perimetric dimensions of the opening in the buoyant frame, said buoyant substructure base member having a top face, said buoyant substructure at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (d) positioning said buoyant substructure within said opening in said buoyant frame; (e) connecting said buoyant frame to a seabed by mooring means; (f) submerging said buoyant frame below the water surface to a predetermined design depth; (g) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure; (h) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (i) lowering lifting means from at least one lifting device located on the self-floating deck structure and connecting the lifting means to the buoyant substructure; (j) activating at least one lifting device to retract the lifting means and lift the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (k) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (l) deballasting the buoyant substructure until the top face of the buoyant substructure base member mates with the buoyant frame bottom surface; (m) connecting said buoyant frame to said buoyant substructure by welding or by one or more mechanical device; (n) raising the self-floating deck to a predetermined elevation above the water surface by adjusting said mooring means or by deballasting said buoyant substructure or said buoyant frame.
 117. The method to claim 116 wherein said lifting means is drill pipe, chain, cable, wire or rope.
 118. The method according to claim 116 wherein said lifting device is a drilling rig, winch, jack or crane.
 119. The method according to claim 116 wherein said buoyant substructure is suspended from the self-floating deck structure by at least one chain, cable, wire or rope when said buoyant substructure is ballasted below said water surface.
 120. The method according to claim 116 wherein a stopping means is positioned on said buoyant substructure sidewall, said stopping means prevents said buoyant substructure from passing through said opening in said buoyant frame.
 121. The method according to claim 120 wherein said stopping means is sized and shaped to support the submerged buoyant substructure when said stopping means rests on the buoyant frame top surface.
 122. The method according to claim 121 wherein said buoyant substructure is ballasted down below said water surface until said stopping means rests on said buoyant frame top surface.
 123. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming a circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity present in the self-floating deck structure; (c) providing a buoyant frame that is capable of being fully submerged below the water surface, said buoyant frame having a buoyant frame top surface and a buoyant frame bottom surface, said buoyant frame further having a plurality of openings extending through said buoyant frame from said buoyant frame top surface to said buoyant frame bottom surface, said openings being sized and shaped to allow a deck support leg to be positioned within said opening; (d) positioning each deck support leg within an opening in said buoyant frame; (e) connecting said buoyant frame to a seabed by mooring means; (f) submerging said buoyant frame below the water surface at a predetermined design depth; (g) positioning said self-floating deck structure adjacent to said buoyant substructure; (h) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure; (i) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg is below the bottom surface of the self-floating deck structure; (j) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface present on the buoyant substructure; (k) activating at least one lifting device to retract the connected lifting line and lift the buoyant substructure up until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface; (l) connecting the self-floating deck structure to the buoyant substructure by welding or by a plurality of mechanical devices; (m) deballasting the buoyant substructure until the top face of the buoyant substructure base member mates with the buoyant frame bottom surface; (n) connecting said buoyant frame to said buoyant substructure by welding one or more mechanical device; and (o) raising the self-floating deck structure to a predetermined elevation above the water surface by adjusting said mooring means or deballasting said buoyant substructure or said buoyant frame.
 124. The method according to claim 123 wherein the lifting line is a chain, cable, wire or rope.
 125. The method according to claim 123 wherein the lifting device is a drilling rig, winch, jack or crane.
 126. The method according to claim 123 wherein said buoyant substructure is suspended from the self-floating deck structure by at least one chain, cable, wire or rope when said buoyant substructure is ballasted below said water surface.
 127. The method according to claim 123 wherein said buoyant substructure is suspended from the self-floating deck structure by at least one lifting line connected to at least one lifting device.
 128. The method according to claim 123 wherein a stopping means is positioned on at least one deck support leg sidewall, said stopping means being sized and shaped such that said stopping means prevents said deck support legs from passing through said openings in said buoyant frame.
 129. The method according to claim 128 wherein said stopping means are sized and shaped to support the submerged buoyant substructure when said stopping means rest on the buoyant frame top surface.
 130. The method according to claim 129 wherein said buoyant substructure is ballasted down below said water surface until at least one stopping means rest on said buoyant frame top surface.
 131. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure with a bottom surface and a plurality of recessed cavities extending upward from said bottom surface of the self-floating deck structure, each of said recessed cavities comprising an open end, at least one recessed cavity sidewall and a recessed cavity ceiling surface, each of said recessed cavity ceiling surfaces being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck structure forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, and that is capable of being fully submerged below the water surface, each deck support leg having a deck support leg top surface and at least one deck support leg sidewall, the intersection of each deck support leg top surface and each deck support leg sidewall forming a circumferential edge of the deck support leg, each deck support leg top surface and the deck support leg sidewall adjacent to said deck support leg top surface being adapted and sized to fit within a recessed cavity present in the self-floating deck structure; (c) providing a buoyant frame that is capable of being fully submerged below the water surface, said buoyant frame having a buoyant frame top surface and a buoyant frame bottom surface, said buoyant frame further having a plurality of openings extending through said buoyant frame from said buoyant frame top surface to said buoyant frame bottom surface, said openings being sized and shaped to allow a deck support leg through said opening; (d) positioning each deck support leg within an opening in said buoyant frame; (e) connecting said buoyant frame to a seabed by mooring means; (f) submerging said buoyant frame below the water surface to a predetermined design depth; (g) ballasting the buoyant substructure below the water surface until the deck support leg top surface of each deck support leg is below the bottom surface of the self-floating deck structure; (h) positioning the self-floating deck structure over the buoyant substructure so that each of the recessed cavities of the self-floating deck structure are aligned over a deck support leg top surface present on the buoyant substructure; (i) lowering lifting means from at least one lifting device located on the self-floating deck structure and connecting the lifting means to the buoyant substructure; (j) activating at least one lifting device to retract the lifting means and lift the buoyant substructure up until each deck support leg top surface is inserted into a recessed cavity of the self-floating deck structure and each deck support leg top surface mates with a recessed cavity ceiling surface at a point above the water surface; (k) connecting the self-floating deck structure to the buoyant substructure by welding or by a plurality of mechanical devices; (l) deballasting the buoyant substructure until the top face of the buoyant substructure base member mates with the buoyant frame bottom surface; (m) connecting said buoyant frame to said buoyant substructure by welding or one or more mechanical device; and (n) raising the self-floating deck to a predetermined elevation above the water surface by adjusting said mooring means or deballasting said buoyant substructure or said buoyant frame.
 132. The method according to claim 130 wherein said lifting means is drill pipe, chain, cable, wire or rope.
 133. The method according to claim 130 wherein said lifting device is a drilling rig, winch, jack or crane.
 134. The method according to claim 131 wherein said buoyant substructure is suspended from the self-floating deck structure by at least one chain, cable, wire or rope when said buoyant substructure is ballasted below said water surface.
 135. The method according to claim 131 wherein a stopping means is positioned on at least one deck support leg sidewall, the circumferential dimension of said stopping means being sized and shaped such that said stopping means prevents said deck support legs from passing through said openings in said buoyant frame.
 136. The method according to claim 135 wherein said stopping means are sized and shaped to support the submerged buoyant substructure when said stopping means rest on the buoyant frame top surface.
 137. The method according to claim 136 wherein said buoyant substructure is ballasted down below said water surface until at least one stopping means rest on said buoyant frame top surface.
 138. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity; (b) providing a base structure that is capable of being fully submerged below the water surface, said base structure having a base structure top surface and a base structure bottom surface, said base structure further having a base structure opening extending through said base structure from said base structure top surface to said base structure bottom surface, said base structure opening being sized and shaped to allow a buoyant substructure to be positioned within said base structure opening, said base structure further comprising a hollow tube extending upward from said base structure top surface in vertical alignment with said base structure opening; (c) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface, said buoyant substructure further having a buoyant substructure base member that has perimetric dimensions greater than the perimetric dimensions of the opening in the buoyant frame, said buoyant substructure base member having a top face, said buoyant substructure having at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (d) positioning said buoyant substructure within said hollow tube and connecting said buoyant substructure to said base structure with connecting means; (e) positioning said base structure on the seabed at an installation site; (f) securing said base structure to said seabed; (g) positioning said self-floating deck structure adjacent to said buoyant substructure; (h) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure; (i) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure; (j) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (k) activating at least one lifting device to retract the connected lifting line and lifting the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (l) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; (m) raising the self-floating deck structure to a predetermined elevation above the water surface by deballasting said buoyant substructure; and (n) connecting said buoyant substructure to said hollow tube by grouting, welding or by one or mechanical connector.
 139. The method according to claim 138 wherein said lifting line is a chain, cable, wire or rope.
 140. The method according to claim 138 wherein said lifting device is a drilling rig, winch, jack or crane.
 141. The method according to claim 138 wherein said connecting means is a mechanical connector or one or more tension member.
 142. The method according to claim 141 wherein said tension member is a chain, a cable or a pipe.
 143. The method according to claim 138 wherein said base structure bottom surface extends across said base structure opening.
 144. The method according to claim 138 wherein said base structure is buoyant.
 145. The method according to claim 138 wherein said hollow tube is cylindrical or rectangular.
 146. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface and a recessed cavity extending upward from said bottom surface of the self-floating deck structure, said recessed cavity comprising an open end, at least one recessed cavity sidewall, and a recessed cavity ceiling surface, said recessed cavity ceiling surface being positioned above a water surface, the intersection of the recessed cavity sidewall and the recessed cavity ceiling surface forming at least one upper circumferential edge of the recessed cavity, and the intersection of the recessed cavity sidewall and the bottom surface of the self-floating deck forming at least one lower circumferential edge of the recessed cavity; (b) providing a buoyant frame that is capable of being fully submerged below the water surface, said buoyant frame having a buoyant frame top surface and a buoyant frame bottom surface, said buoyant frame further having an opening extending through said buoyant frame top surface to said buoyant frame bottom surface, said opening being sized and shaped to allow a buoyant substructure to be positioned within said opening, said buoyant frame further having a hollow tube extending upward from said buoyant frame top surface in vertical alignment with said opening; (c) providing a buoyant substructure that is capable of being fully submerged below the water surface, said buoyant substructure having a buoyant substructure top surface, said buoyant substructure further having a buoyant substructure base member that has perimetric dimensions greater than the perimetric dimensions of the opening in the buoyant frame, said buoyant substructure base member having a top face, said buoyant substructure having at least one buoyant substructure sidewall, the intersection of the buoyant substructure top surface and the buoyant substructure sidewall forming an upper circumferential edge of the buoyant substructure, the buoyant substructure top surface and the buoyant substructure sidewall adjacent to the buoyant substructure top surface being adapted and sized to fit within the recessed cavity of the self-floating deck structure; (d) positioning said buoyant substructure at least partially within said hollow tube; (e) connecting said buoyant frame to a seabed by mooring means; (f) submerging said buoyant frame below the water surface at a predetermined design depth; (g) positioning said self-floating deck structure adjacent to said buoyant substructure; (h) lowering at least one lifting line connected to at least one lifting device located on the self-floating deck structure and connecting each lifting line to the buoyant substructure; (i) ballasting the buoyant substructure below the water surface until the buoyant substructure top surface is below the bottom surface of the self-floating deck structure; (j) positioning the self-floating deck structure over the buoyant substructure so that the recessed cavity of the self-floating deck structure is aligned over the buoyant substructure top surface; (k) activating at least one lifting device to retract the connected lifting line and lifting the buoyant substructure top surface up into the recessed cavity until the buoyant substructure top surface mates with the recessed cavity ceiling surface at a point above the water surface; (l) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; (m) raising the self-floating deck structure to a predetermined elevation above the water surface by adjusting said mooring means or deballasting said buoyant substructure or buoyant frame; and (n) connecting said buoyant substructure to said hollow tube by grouting, welding or by one or mechanical connector.
 147. The method according to claim 146 wherein the lifting line is a chain, cable, wire or rope.
 148. The method according to claim 146 wherein the lifting device is a drilling rig, winch, jack or crane.
 149. The method according to claim 146 wherein said buoyant frame bottom surface extends across said opening in said buoyant frame.
 150. The method according to claim 146 wherein said hollow tube is cylindrical or rectangular.
 151. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface, said self-floating deck structure having at least two hulls extending from the bottom surface, said hulls being sized and shaped to provide buoyancy for the self-floating deck such that the bottom surface is positioned above the water surface, said hulls further being sized and shaped such that the self-floating deck structure can be positioned over a buoyant substructure such that the bottom surface of the self-floating deck structure does not collide with a buoyant substructure top surface; (b) providing a buoyant substructure, said buoyant substructure having a buoyant substructure top surface and a buoyant substructure bottom surface, said buoyant substructure top surface and buoyant substructure bottom surface being connected by at least one buoyant substructure sidewall; (c) positioning said self-floating deck structure over said buoyant substructure; (d) lowering at least one lifting means connected to at least one lifting device located on the self-floating deck structure and connecting each lifting means to the buoyant substructure; (e) activating at least one lifting device to retract the connected lifting means and lift the buoyant substructure top surface up until the buoyant substructure top surface mates with the bottom surface of the self-floating deck structure; (f) connecting the self-floating deck structure to the buoyant substructure by welding or by one or more mechanical devices; and (g) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 152. The method according to claim 151 wherein the lifting means is drill pipe, chain, wire, cable, or rope.
 153. The method according to claim 151 wherein the lifting device is a winch, jack, drilling rig or crane.
 154. A method for installing a self-floating deck structure onto a buoyant substructure, said method comprising the steps of: (a) providing a self-floating deck structure having a bottom surface, said self-floating deck structure having at least two hulls extending from the bottom surface, said hulls being sized and shaped to provide buoyancy for the self-floating deck such that the bottom surface is positioned above the water surface, said hulls further being sized and shaped such that the self-floating deck structure can be positioned over a buoyant substructure such that the bottom surface of the self-floating deck structure does not collide with a buoyant substructure top surface; (b) providing a buoyant substructure having a buoyant substructure bottom surface and a plurality of deck support legs, each deck support leg having a deck support leg top surface; (c) positioning said self-floating deck structure over said deck support legs of said buoyant substructure; (d) connecting at least one lifting means connected to at least one lifting device located on the self-floating deck structure to the buoyant substructure; (e) activating at least one lifting device to retract the lifting means and lift the buoyant substructure up until each deck support leg top surface mates with the bottom surface of the self-floating deck structure; (f) connecting the self-floating deck structure to the buoyant substructure by welding or by a plurality of mechanical devices; and (g) deballasting the buoyant substructure to raise the self-floating deck structure to a predetermined elevation above the water surface.
 155. The method according to claim 154 wherein the lifting means is drill pipe, chain, wire, cable, or a rope.
 156. The method according to claim 154 wherein the lifting device is a winch, jack, drilling rig or crane. 